Abstract

Enhancement of light extraction efficiency (LEE) of AlGaN-based deep-ultraviolet (DUV) light emitting diodes (LEDs) has been attempted by adopting Ag-nanodots/Al reflective electrodes on a highly transparent complex p-type layer. By thinning the p-GaN to several nm, highly DUV transparent p-type layer is achieved, making it meaningful for the application of reflective electrodes composed of Ag-nanodots and Al film to allow most light emitted upward to be reflected back to the sapphire side. By this approach, the maximum light output power and external quantum efficiency of the DUV-LEDs with optimized Ag nanodots/Al electrodes are severally increased by 52% and 58%, respectively, compared to those with traditional Ni/Au electrodes when the current is below 200 mA.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

In recent years, AlGaN-based solid-state deep ultraviolet (DUV) light emitting diodes (LEDs) have attracted much attention because of their extensive application in air and water purification, sterilization, DUV curing, and so on [1,2]. Compared with traditional gas DUV light sources, such as mercury lamps, AlGaN-based DUV-LEDs are considered to have many advantages such as small size, high power, low energy consumption, and environment friendly, etc., thus being a kind of promising DUV light source. Especially, the recent outbreak of the COVID-19 around the world further evokes the passion to apply DUV light irradiation to kill the virus [3], hence the realization of high-performance AlGaN-based DUV-LEDs becomes more urgent and essential. To date, a great progress has been achieved for AlGaN-based DUV-LEDs, and the external quantum efficiency (EQE) as high as 20.3% has been realized, whereas the performance of AlGaN-based DUV-LEDs still remains at a relatively low level compared to commercial GaN-based visible LEDs [46]. As is well known, the EQE is determined by the internal quantum efficiency (IQE), carrier injection efficiency (CIE), and light extraction efficiency (LEE). Up to now, high IQE and CIE have been realized [7,8], however the effective ways to increase LEE are very limited [9], which thus becomes the biggest obstacle hindering the improvement of the EQE [10,11]. Therefore, it is very important to develop effective approaches to promote the light extraction effectively.

For AlGaN-based DUV-LEDs, the main factors that hinder the improvement of LEE are the optical polarization characteristics [12,13], total reflection at the interface [14], and strong absorption of DUV light by the p-GaN layer, which are all serious challenges at present [15,16]. In order to improve the LEE, many researchers have made great efforts. For example, Liu et al. used AlN-delta-GaN quantum well to achieve a large transverse electric (TE)-polarized emission, thus improving the light polarization [17]. Wang et al. weakened the total reflection at the interface of sapphire and air and enhanced the light extraction angle by using a moth-eye microstructure [18]. And enhanced light extraction was also achieved by high-reflectance metals [19,20], reflective photonic crystals (PCs) [9], distributed Bragg reflectors [21] or omnidirectional reflectors [22]. Especially interestingly, Maeda et al. adopted a transparent p-AlGaN contact layer and highly reflective Ni/Mg, Rh, Ni/Al as the p-electrodes to obtain higher LEE, showing a great potential for high performance DUV-LED devices [23,24]. However, due to the difficulties to obtain p-AlGaN with high hole concentration, poor Ohmic contact with the p-AlGaN layer remains a big obstacle, as it leads to an increasing working voltage and decreased device stability as well as device life. Therefore, it is of great significance to seek for an optimized structure which can balance the light extraction and electrical properties.

In this study, a novel approach that can effectively enhance the light extraction and meanwhile maintain the acceptable electrical properties of AlGaN-based DUV-LEDs has been achieved by combining an Ag nanodots/Al reflective electrode with a highly transparent complex p-type layer. The p-type layer is composed of a p-AlGaN layer and a p-GaN layer with a thickness of several nm, which can greatly reduce the DUV light absorption. The Ag nanodots can ensure good Ohmic contacts with p-GaN, and the area without Ag nanodots can improve the reflectivity of DUV light through Al film. Based on such a complex p-type layer, a highly reflective p-electrode comprising Ag nanodots and Al film is adopted to maintain the electrical properties and enhance the light extraction.

Two schematic DUV-LED device structures used in this study are shown in Fig. 1 for comparison, including one with the proposed structure (defined as structure A) and another one with commonly used Ni/Au electrodes structure (defined as structure B). The DUV-LED wafers were firstly grown on (0001) sapphire substrates by a 3×2′′ close-coupled-showerhead (CCS) Aixtron metal-organic chemical vapor deposition (MOCVD) system. At beginning, a 1.5-μm-thick AlN buffer layer was grown and followed by a 0.5-μm-thick AlN/AlGaN stress modulation multilayer and a 1.5-μm-thick n-Al0.55Ga0.45N layer (n∼2.5×1018 cm−3) in sequence. Then, the active region with five pairs of nominally Al0.37Ga0.63N quantum well layer and Si-doped Al0.5Ga0.5N barrier layer (n∼1.0×1018 cm−3) was grown. Subsequently, a 10-nm-thick Mg-doped AlGaN electron blocking layer and a 96-nm-thick Mg-doped (∼1.5×1019 cm−3) p-Al0.4Ga0.6N/Al0.67Ga0.33N superlattice were grown. Finally, a thin Mg-doped p-GaN (p∼1.0×1018 cm−3) layer was grown as the Ohmic contact layer.

 

Fig. 1. Schematic structures of DUV-LEDs with (a) Ag nanodots/Al electrodes and (b) Ni/Au electrodes.

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After the growth, device fabrication for structures A and B was conducted respectively, while the process was consistent except for the p-type electrodes. Firstly, the wafers were fabricated by inductively coupled plasma (ICP) etching to expose the n-AlGaN region, and then Ti/Al/Ni/Au metals were evaporated. Subsequently, the samples were annealed in a N2 atmosphere at 850 ℃ for 35 s to form Ohmic contacts. After that, 4-nm-thick Ag was deposited on the p-GaN layer for structure A, followed by annealing in a N2 atmosphere to form Ag nanodots. Then, 150-nm-thick Al film was evaporated on the Ag nanodots region to complete the complex Ag nanodots/Al p-type electrodes. For comparison, Ni/Au metals were evaporated as the p-type electrodes for structure B. Finally, a flip-chip technology was applied to obtain the DUV-LED devices with the size of 889×889 μm2 without adopting any special light extraction and packaging. The device performance was measured by an integrating sphere from EVERFINE Corporation. Besides, to evaluate the electrical properties of the p-electrodes, the transmission line method (TLM) patterns with 10 ∼ 40 μm gaps were defined using photolithography.

Morphology evolution of Ag film is firstly studied under different annealing conditions on the p-GaN layer, before depositing the Al layer. Figure 2(a) shows the surface scanning electron microscopy (SEM) image after annealing at 300 ℃ for 3 minutes. It can be seen that Ag tends to form small particles with a diameter varying from 20 to 100 nm. With further increasing the annealing temperature to 400 ℃ for 3 minutes, the Ag nanodots become larger and the diameter varies from 50 to 200 nm as shown in Fig. 2(b). Figure 2(c) further shows the surface morphology evolution with temperature increasing to 500 ℃ just for 1 minute. The reason for choosing 1 minute lies in the fact that Ag cannot withstand such high temperature for a long time. It can be noted that the particles shown in Fig. 2(c) become much larger than those in Figs. 2(a) and 2(b), clearly presenting strong size dependence on the annealing conditions. To check the transmittance of the Ag nanodots for DUV light, Ag film was deposited on a double-polished sapphire and then annealed under the conditions as mentioned above for evaluation. The Ag nanodots also form on sapphire, which are similar to the features as shown in Fig. 2(a)–2(c) under different annealing temperatures (not shown here). Figure 2(d) shows the transmittance spectra of Ag nanodots formed on double-polished sapphire under different annealing conditions. It is found that a high transmittance above 80% around the wavelength of 280 nm can be obtained with the annealing temperature varying between 300 and 400 ℃. However, obvious transmittance degradation occurs when the temperature is further increased to 500 ℃.

 

Fig. 2. Morphology evolution of Ag under different annealing conditions: (a) 300 ℃ for 3 minutes, (b) 400 ℃ for 3 minutes, and (c) 500 ℃ for 1 minute. (d) Transmittance spectra of Ag nanodots on sapphire under different annealing conditions.

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We further explore the comprehensive optical characteristics of the complex p-type layer and the p-electrodes for structure A. Figure 3(a) presents the transmission electron microscopy (TEM) image of the p-type layer structure. The thickness of p-GaN is only 7.7 nm. If only one reflection is considered, the transmittance of 7.7-nm thick p-GaN layer is approximately 88% at 280 nm according to the absorption coefficient for GaN [2527]. Figure 3(b) shows atomic force microscopy (AFM) image of this thin p-GaN. It features a smooth surface with clear and straight atomic steps, whose root-mean square (RMS) roughness value is 0.137 nm (3×3 μm2). Moreover, the transmittance of p-AlGaN superlattice structure with hole concentration of 3.7×1018 cm−3 at room temperature (see Supplement 1) used in the DUV-LEDs is also measured. By directly growing the same superlattice structure on an AlN template grown on double-polished sapphire, the transmittance of the p-AlGaN superlattice layer can reach above 92% at 280 nm as shown in Fig. 3(c), presenting a high DUV transparency. Besides, the reflectance of Ag nanodots/Al complex electrodes on double-polished sapphire is also measured, as shown in Fig. 3(d). As can be seen that the reflectivity of this complex electrodes reaches 69% at the wavelength of 280 nm, which is more than twice of that of Ni/Au electrodes at 280 nm (∼30%) [9]. It can thus be expected that the combination of the Ag-nanodots/Al reflective electrodes and highly transparent complex p-type layer will greatly reflect DUV light to the sapphire side.

 

Fig. 3. (a) Cross-sectional TEM image, (b) AFM image of the LED with thin p-GaN. (c) Transmittance of the p-AlGaN superlattice. (d) Reflectivity of the Ag nanodots/Al complex electrodes.

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The electrical characteristics of structures A and B are also compared as shown in Fig. 4(a). It is found that Ohmic contact characteristic occurs in both of these two structures, and the current of sample B with Ni/Au electrodes is higher than that with Ag nanodots/Al electrodes at the same voltage, revealing a certain degree of degradation when adopting Ag nanodots to achieve Ohmic contacts [28]. Figure 4(b) further exhibits the typical I-V characteristics of structures A and B. The forward voltage at the injection current of 20 mA for structure A reaches 9.2 V, which is obviously greater than the value of 7.6 V in structure B. The increased voltage difference of 1.6 V comes from the increased contact resistance between the p-GaN and Ag nanodots/Al electrodes, which possibly originates from the significantly decreased contact area of Ag nanodots on the p-GaN. Compared with the efforts to use reflective electrodes directly on p-AlGaN, such as Rh metal [5], the increased voltage cost of the proposed scheme is significantly reduced, which indicates that the proposed device structure has great potential in maintaining acceptable electrical properties and enhanced light extraction.

 

Fig. 4. (a) Comparison of lateral I-V characteristics of Ni/Au contact and Ag nanodots/Al complex electrodes on p-GaN. (b) The I-V characteristics of DUV-LED structures A and B.

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The device performance adopting these two different electrode structures are further compared. The electroluminescence (EL) spectra at 100 mA for structures A and B present single peak emission with wavelength of 282.6 nm and 280.3 nm, respectively, as shown in Fig. 5(a). Figure 5(b) shows the variation of the full width at half maximum (FWHM) and wavelength peak with the current for structures A and B. The FWHM of DUV-LED structures A and B increases gradually with injection current, and the FWHM of the EL spectra are severally 9.4 nm and 9.5 nm at 100 mA, presenting little difference. Similarly, the wavelength peak also increases gradually with current, from 281.7 nm and 279.6 nm at 5 mA to 283.7 nm and 281 nm at 200 mA for structures A and B, respectively. We also perform the EQE and light output power (LOP) measurement with different injection current, as shown in Fig. 5(c). The EQE increases with the injection current, and reaches the maximum at 20 mA. After that, it decreases. The LOP over the whole current range (0-200 mA) increases with the current, but the increasing speed becomes slower at high current. The maximum LOP and EQE over the whole current range (0-200 mA) for the proposed structure A are severally 11.1 mW and 1.76%, which are significantly increased by 52% and 58% respectively compared to structure B with the commonly used Ni/Au electrodes. These results prove that the proposed approach adopting Ag-nanodots/Al reflective electrodes based on a highly transparent complex p-type layer can significantly improve the LEE and thus device performance of DUV-LEDs as a whole.

 

Fig. 5. (a) The EL spectra of structures A and B at 100 mA. (b) The FWHM and wavelength, and (c) The EQE and LOP of structures A and B under different injection current.

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In summary, enhanced LEE for AlGaN-based DUV-LEDs has been achieved based on a proposed approach that can enhance light extraction and maintain acceptable electrical properties. By thinning the p-GaN layer to several nm, p-type AlGaN/GaN complex layer becomes highly DUV transparent, which makes it possible for the application of reflective electrodes composed of Ag-nanodots and Al film, and thus allow more light emission upward to be reflected to the sapphire side. Applying this approach, the maximum LOP and the EQE of DUV-LEDs with optimized Ag nanodots/Al electrodes are severally increased by 52% and 58% respectively compared to that adopting traditional Ni/Au electrodes.

Funding

National Key Research and Development Program of China (2016YFB0400101, 2018YFE0125700); National Natural Science Foundation of China (61674009, 61974002, 11634002, 61521004, 61927806); Area Research and Development Project of Guangdong Province (2020B010172001); Major Scientific and Technological Innovation Project (MSTIP) of Shandong Province (2019JZZY010209).

Disclosures

The authors declare no conflicts of interest.

See Supplement 1 for supporting content.

References

1. M. Kneissl, III-Nitride Ultraviolet Emitters: Technology and Applications (Springer, 2016), Chap. 1.

2. R. K. Mondal, V. Chatterjee, S. Prasad, and S. Pal, “Suppression of efficiency droop in AlGaN based deep UV LEDs using double side graded electron blocking layer,” Semicond. Sci. Technol. 35(5), 055031 (2020). [CrossRef]  

3. H. Inagaki, A. Saito, H. Sugiyama, T. Okabayashi, and S. Fujimoto, “Rapid inactivation of SARS-CoV-2 with Deep-UV LED irradiation,” Emerging Microbes Infect. 9(1), 1744–1747 (2020). [CrossRef]  

4. H. Hirayama, S. Fujikawa, and N. Kamata, “Recent progress in AlGaN-based deep-UV LEDs,” Electron Comm Jpn 98(5), 1–8 (2015). [CrossRef]  

5. T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017). [CrossRef]  

6. S. H. Chao, L. H. Yeh, R. T. Wu, K. Kawagishi, and S. C. Hsu, “Novel patterned sapphire substrates for enhancing the efficiency of GaN-based light-emitting diodes,” RSC Adv. 10(28), 16284–16290 (2020). [CrossRef]  

7. Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015). [CrossRef]  

8. H. Hirayama, N. Maeda, S. Fujikawa, S. Toyoda, and N. Kamata, “Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light- emitting diodes,” Jpn. J. Appl. Phys. 53(10), 100209 (2014). [CrossRef]  

9. Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018). [CrossRef]  

10. N. Maeda, M. Jo, and H. Hirayama, “Improving the Light-Extraction Efficiency of AlGaN DUV-LEDs by Using a Superlattice Hole Spreading Layer and an Al Reflector,” Phys. Status Solidi A 215(8), 1700436 (2018). [CrossRef]  

11. H. Wan, S. Zhou, S. Lan, and C. Gui, “Light Extraction Efficiency Optimization of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes,” ECS J. Solid State Sci. Technol. 9(4), 046002 (2020). [CrossRef]  

12. C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015). [CrossRef]  

13. H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018). [CrossRef]  

14. D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017). [CrossRef]  

15. H. Y. Ryu, I. G. Choi, H. S. Choi, and J. I. Shim, “Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Express 6(6), 062101 (2013). [CrossRef]  

16. H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016). [CrossRef]  

17. C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018). [CrossRef]  

18. S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018). [CrossRef]  

19. H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009). [CrossRef]  

20. N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010). [CrossRef]  

21. T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013). [CrossRef]  

22. S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017). [CrossRef]  

23. N. Maeda, J. Yun, M. Jo, and H. Hirayama, “Enhancing the light-extraction efficiency of AlGaN deep-ultraviolet light-emitting diodes using highly reflective Ni/Mg and Rh as p-type electrodes,” Jpn. J. Appl. Phys. 57(4S), 04FH08 (2018). [CrossRef]  

24. N. Maeda, M. Jo, and H. Hirayama, “Improving the Efficiency of AlGaN Deep-UV LEDs by Using Highly Reflective Ni/Al p-Type Electrodes,” Phys. Status Solidi A 215(8), 1700435 (2018). [CrossRef]  

25. Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).

26. G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997). [CrossRef]  

27. J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997). [CrossRef]  

28. W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018). [CrossRef]  

References

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  1. M. Kneissl, III-Nitride Ultraviolet Emitters: Technology and Applications (Springer, 2016), Chap. 1.
  2. R. K. Mondal, V. Chatterjee, S. Prasad, and S. Pal, “Suppression of efficiency droop in AlGaN based deep UV LEDs using double side graded electron blocking layer,” Semicond. Sci. Technol. 35(5), 055031 (2020).
    [Crossref]
  3. H. Inagaki, A. Saito, H. Sugiyama, T. Okabayashi, and S. Fujimoto, “Rapid inactivation of SARS-CoV-2 with Deep-UV LED irradiation,” Emerging Microbes Infect. 9(1), 1744–1747 (2020).
    [Crossref]
  4. H. Hirayama, S. Fujikawa, and N. Kamata, “Recent progress in AlGaN-based deep-UV LEDs,” Electron Comm Jpn 98(5), 1–8 (2015).
    [Crossref]
  5. T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
    [Crossref]
  6. S. H. Chao, L. H. Yeh, R. T. Wu, K. Kawagishi, and S. C. Hsu, “Novel patterned sapphire substrates for enhancing the efficiency of GaN-based light-emitting diodes,” RSC Adv. 10(28), 16284–16290 (2020).
    [Crossref]
  7. Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
    [Crossref]
  8. H. Hirayama, N. Maeda, S. Fujikawa, S. Toyoda, and N. Kamata, “Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light- emitting diodes,” Jpn. J. Appl. Phys. 53(10), 100209 (2014).
    [Crossref]
  9. Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
    [Crossref]
  10. N. Maeda, M. Jo, and H. Hirayama, “Improving the Light-Extraction Efficiency of AlGaN DUV-LEDs by Using a Superlattice Hole Spreading Layer and an Al Reflector,” Phys. Status Solidi A 215(8), 1700436 (2018).
    [Crossref]
  11. H. Wan, S. Zhou, S. Lan, and C. Gui, “Light Extraction Efficiency Optimization of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes,” ECS J. Solid State Sci. Technol. 9(4), 046002 (2020).
    [Crossref]
  12. C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
    [Crossref]
  13. H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018).
    [Crossref]
  14. D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
    [Crossref]
  15. H. Y. Ryu, I. G. Choi, H. S. Choi, and J. I. Shim, “Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Express 6(6), 062101 (2013).
    [Crossref]
  16. H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
    [Crossref]
  17. C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018).
    [Crossref]
  18. S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
    [Crossref]
  19. H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
    [Crossref]
  20. N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
    [Crossref]
  21. T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
    [Crossref]
  22. S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
    [Crossref]
  23. N. Maeda, J. Yun, M. Jo, and H. Hirayama, “Enhancing the light-extraction efficiency of AlGaN deep-ultraviolet light-emitting diodes using highly reflective Ni/Mg and Rh as p-type electrodes,” Jpn. J. Appl. Phys. 57(4S), 04FH08 (2018).
    [Crossref]
  24. N. Maeda, M. Jo, and H. Hirayama, “Improving the Efficiency of AlGaN Deep-UV LEDs by Using Highly Reflective Ni/Al p-Type Electrodes,” Phys. Status Solidi A 215(8), 1700435 (2018).
    [Crossref]
  25. Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).
  26. G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
    [Crossref]
  27. J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
    [Crossref]
  28. W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018).
    [Crossref]

2020 (4)

R. K. Mondal, V. Chatterjee, S. Prasad, and S. Pal, “Suppression of efficiency droop in AlGaN based deep UV LEDs using double side graded electron blocking layer,” Semicond. Sci. Technol. 35(5), 055031 (2020).
[Crossref]

H. Inagaki, A. Saito, H. Sugiyama, T. Okabayashi, and S. Fujimoto, “Rapid inactivation of SARS-CoV-2 with Deep-UV LED irradiation,” Emerging Microbes Infect. 9(1), 1744–1747 (2020).
[Crossref]

S. H. Chao, L. H. Yeh, R. T. Wu, K. Kawagishi, and S. C. Hsu, “Novel patterned sapphire substrates for enhancing the efficiency of GaN-based light-emitting diodes,” RSC Adv. 10(28), 16284–16290 (2020).
[Crossref]

H. Wan, S. Zhou, S. Lan, and C. Gui, “Light Extraction Efficiency Optimization of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes,” ECS J. Solid State Sci. Technol. 9(4), 046002 (2020).
[Crossref]

2018 (8)

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

N. Maeda, M. Jo, and H. Hirayama, “Improving the Light-Extraction Efficiency of AlGaN DUV-LEDs by Using a Superlattice Hole Spreading Layer and an Al Reflector,” Phys. Status Solidi A 215(8), 1700436 (2018).
[Crossref]

H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018).
[Crossref]

C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018).
[Crossref]

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

N. Maeda, J. Yun, M. Jo, and H. Hirayama, “Enhancing the light-extraction efficiency of AlGaN deep-ultraviolet light-emitting diodes using highly reflective Ni/Mg and Rh as p-type electrodes,” Jpn. J. Appl. Phys. 57(4S), 04FH08 (2018).
[Crossref]

N. Maeda, M. Jo, and H. Hirayama, “Improving the Efficiency of AlGaN Deep-UV LEDs by Using Highly Reflective Ni/Al p-Type Electrodes,” Phys. Status Solidi A 215(8), 1700435 (2018).
[Crossref]

W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018).
[Crossref]

2017 (3)

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
[Crossref]

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
[Crossref]

2016 (1)

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

2015 (3)

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
[Crossref]

H. Hirayama, S. Fujikawa, and N. Kamata, “Recent progress in AlGaN-based deep-UV LEDs,” Electron Comm Jpn 98(5), 1–8 (2015).
[Crossref]

2014 (1)

H. Hirayama, N. Maeda, S. Fujikawa, S. Toyoda, and N. Kamata, “Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light- emitting diodes,” Jpn. J. Appl. Phys. 53(10), 100209 (2014).
[Crossref]

2013 (2)

H. Y. Ryu, I. G. Choi, H. S. Choi, and J. I. Shim, “Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Express 6(6), 062101 (2013).
[Crossref]

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

2010 (1)

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

2009 (1)

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

1997 (2)

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
[Crossref]

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Akasaki, I.

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Amano, H.

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Bryan, I.

Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
[Crossref]

Bryan, Z.

Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
[Crossref]

Casey, H. C.

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Chao, S. H.

S. H. Chao, L. H. Yeh, R. T. Wu, K. Kawagishi, and S. C. Hsu, “Novel patterned sapphire substrates for enhancing the efficiency of GaN-based light-emitting diodes,” RSC Adv. 10(28), 16284–16290 (2020).
[Crossref]

Chatterjee, V.

R. K. Mondal, V. Chatterjee, S. Prasad, and S. Pal, “Suppression of efficiency droop in AlGaN based deep UV LEDs using double side graded electron blocking layer,” Semicond. Sci. Technol. 35(5), 055031 (2020).
[Crossref]

Chen, C.

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018).
[Crossref]

Chen, J.

H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018).
[Crossref]

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

Chen, W.

W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018).
[Crossref]

Chen, X.

Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).

Choi, H. S.

H. Y. Ryu, I. G. Choi, H. S. Choi, and J. I. Shim, “Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Express 6(6), 062101 (2013).
[Crossref]

Choi, I. G.

H. Y. Ryu, I. G. Choi, H. S. Choi, and J. I. Shim, “Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Express 6(6), 062101 (2013).
[Crossref]

Collazo, R.

Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
[Crossref]

Dai, J.

H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018).
[Crossref]

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

DenBaars, S. P.

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Do Lee, G.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Egawa, T.

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
[Crossref]

Einfeldt, S.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

Feneberg, M.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Feng, Z. C.

Fujikawa, S.

H. Hirayama, S. Fujikawa, and N. Kamata, “Recent progress in AlGaN-based deep-UV LEDs,” Electron Comm Jpn 98(5), 1–8 (2015).
[Crossref]

H. Hirayama, N. Maeda, S. Fujikawa, S. Toyoda, and N. Kamata, “Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light- emitting diodes,” Jpn. J. Appl. Phys. 53(10), 100209 (2014).
[Crossref]

Fujimoto, S.

H. Inagaki, A. Saito, H. Sugiyama, T. Okabayashi, and S. Fujimoto, “Rapid inactivation of SARS-CoV-2 with Deep-UV LED irradiation,” Emerging Microbes Infect. 9(1), 1744–1747 (2020).
[Crossref]

Goldhahn, R.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Gui, C.

H. Wan, S. Zhou, S. Lan, and C. Gui, “Light Extraction Efficiency Optimization of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes,” ECS J. Solid State Sci. Technol. 9(4), 046002 (2020).
[Crossref]

Guo, Y.

Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).

Guttmann, M.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Ha, K.

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
[Crossref]

Hirayama, H.

N. Maeda, J. Yun, M. Jo, and H. Hirayama, “Enhancing the light-extraction efficiency of AlGaN deep-ultraviolet light-emitting diodes using highly reflective Ni/Mg and Rh as p-type electrodes,” Jpn. J. Appl. Phys. 57(4S), 04FH08 (2018).
[Crossref]

N. Maeda, M. Jo, and H. Hirayama, “Improving the Efficiency of AlGaN Deep-UV LEDs by Using Highly Reflective Ni/Al p-Type Electrodes,” Phys. Status Solidi A 215(8), 1700435 (2018).
[Crossref]

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

N. Maeda, M. Jo, and H. Hirayama, “Improving the Light-Extraction Efficiency of AlGaN DUV-LEDs by Using a Superlattice Hole Spreading Layer and an Al Reflector,” Phys. Status Solidi A 215(8), 1700436 (2018).
[Crossref]

T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
[Crossref]

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

H. Hirayama, S. Fujikawa, and N. Kamata, “Recent progress in AlGaN-based deep-UV LEDs,” Electron Comm Jpn 98(5), 1–8 (2015).
[Crossref]

H. Hirayama, N. Maeda, S. Fujikawa, S. Toyoda, and N. Kamata, “Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light- emitting diodes,” Jpn. J. Appl. Phys. 53(10), 100209 (2014).
[Crossref]

Hoppe, M.

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

Hsu, S. C.

S. H. Chao, L. H. Yeh, R. T. Wu, K. Kawagishi, and S. C. Hsu, “Novel patterned sapphire substrates for enhancing the efficiency of GaN-based light-emitting diodes,” RSC Adv. 10(28), 16284–16290 (2020).
[Crossref]

Hu, J.

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

Ichikawa, T.

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Il Kim, Y.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Inagaki, H.

H. Inagaki, A. Saito, H. Sugiyama, T. Okabayashi, and S. Fujimoto, “Rapid inactivation of SARS-CoV-2 with Deep-UV LED irradiation,” Emerging Microbes Infect. 9(1), 1744–1747 (2020).
[Crossref]

Ishikawa, H.

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
[Crossref]

Islam, S. M.

C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018).
[Crossref]

Iwai, T.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Iwaya, M.

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Jang, J.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Jena, D.

C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018).
[Crossref]

Jeong, J.

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
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Jimbo, T.

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
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Jin, L.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Jo, M.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

N. Maeda, M. Jo, and H. Hirayama, “Improving the Light-Extraction Efficiency of AlGaN DUV-LEDs by Using a Superlattice Hole Spreading Layer and an Al Reflector,” Phys. Status Solidi A 215(8), 1700436 (2018).
[Crossref]

N. Maeda, J. Yun, M. Jo, and H. Hirayama, “Enhancing the light-extraction efficiency of AlGaN deep-ultraviolet light-emitting diodes using highly reflective Ni/Mg and Rh as p-type electrodes,” Jpn. J. Appl. Phys. 57(4S), 04FH08 (2018).
[Crossref]

N. Maeda, M. Jo, and H. Hirayama, “Improving the Efficiency of AlGaN Deep-UV LEDs by Using Highly Reflective Ni/Al p-Type Electrodes,” Phys. Status Solidi A 215(8), 1700435 (2018).
[Crossref]

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

Kamata, N.

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

H. Hirayama, S. Fujikawa, and N. Kamata, “Recent progress in AlGaN-based deep-UV LEDs,” Electron Comm Jpn 98(5), 1–8 (2015).
[Crossref]

H. Hirayama, N. Maeda, S. Fujikawa, S. Toyoda, and N. Kamata, “Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light- emitting diodes,” Jpn. J. Appl. Phys. 53(10), 100209 (2014).
[Crossref]

Kamimura, R.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Kamiyama, S.

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Kan, H.

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Kanazawa, Y.

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

Kashima, Y.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Kawagishi, K.

S. H. Chao, L. H. Yeh, R. T. Wu, K. Kawagishi, and S. C. Hsu, “Novel patterned sapphire substrates for enhancing the efficiency of GaN-based light-emitting diodes,” RSC Adv. 10(28), 16284–16290 (2020).
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Keller, B. P.

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Kim, D.

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
[Crossref]

Kim, J.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Kim, J. K.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Kim, K. K.

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
[Crossref]

Kim, S. J.

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
[Crossref]

Knauer, A.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

Kneissl, M.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

M. Kneissl, III-Nitride Ultraviolet Emitters: Technology and Applications (Springer, 2016), Chap. 1.

Kokubo, M.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Kolbas, R. M.

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Kueller, V.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Kuhn, C.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Kuo, H. C.

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

Kuwabara, M.

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Lan, S.

H. Wan, S. Zhou, S. Lan, and C. Gui, “Light Extraction Efficiency Optimization of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes,” ECS J. Solid State Sci. Technol. 9(4), 046002 (2020).
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Lapeyrade, M.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Lee, D.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Lee, J.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Lee, J. H.

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Lee, J. W.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Lee, K. J.

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
[Crossref]

Li, J.

Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).

Liang, R.

Liu, C.

C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018).
[Crossref]

Lobo, N.

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

Long, H.

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018).
[Crossref]

Maeda, N.

N. Maeda, M. Jo, and H. Hirayama, “Improving the Light-Extraction Efficiency of AlGaN DUV-LEDs by Using a Superlattice Hole Spreading Layer and an Al Reflector,” Phys. Status Solidi A 215(8), 1700436 (2018).
[Crossref]

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

N. Maeda, M. Jo, and H. Hirayama, “Improving the Efficiency of AlGaN Deep-UV LEDs by Using Highly Reflective Ni/Al p-Type Electrodes,” Phys. Status Solidi A 215(8), 1700435 (2018).
[Crossref]

N. Maeda, J. Yun, M. Jo, and H. Hirayama, “Enhancing the light-extraction efficiency of AlGaN deep-ultraviolet light-emitting diodes using highly reflective Ni/Mg and Rh as p-type electrodes,” Jpn. J. Appl. Phys. 57(4S), 04FH08 (2018).
[Crossref]

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

H. Hirayama, N. Maeda, S. Fujikawa, S. Toyoda, and N. Kamata, “Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light- emitting diodes,” Jpn. J. Appl. Phys. 53(10), 100209 (2014).
[Crossref]

Matsumoto, T.

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

Matsuura, E.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Mehnke, F.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Mino, T.

T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
[Crossref]

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

Mishra, U. K.

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Mita, S.

Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
[Crossref]

Mondal, R. K.

R. K. Mondal, V. Chatterjee, S. Prasad, and S. Pal, “Suppression of efficiency droop in AlGaN based deep UV LEDs using double side graded electron blocking layer,” Semicond. Sci. Technol. 35(5), 055031 (2020).
[Crossref]

Mori, F.

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Morita, T.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Muth, J. F.

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Nakashima, T.

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

Noguchi, N.

T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
[Crossref]

Noh, H. S.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Oh, S.

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
[Crossref]

Ohshima, I.

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

Okabayashi, T.

H. Inagaki, A. Saito, H. Sugiyama, T. Okabayashi, and S. Fujimoto, “Rapid inactivation of SARS-CoV-2 with Deep-UV LED irradiation,” Emerging Microbes Infect. 9(1), 1744–1747 (2020).
[Crossref]

Ooi, Y. K.

C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018).
[Crossref]

Osada, Y.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Pal, S.

R. K. Mondal, V. Chatterjee, S. Prasad, and S. Pal, “Suppression of efficiency droop in AlGaN based deep UV LEDs using double side graded electron blocking layer,” Semicond. Sci. Technol. 35(5), 055031 (2020).
[Crossref]

Park, J. H.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Park, S. J.

S. Oh, K. J. Lee, S. J. Kim, K. Ha, J. Jeong, D. Kim, K. K. Kim, and S. J. Park, “Self-assembled indium tin oxide nanoball-embedded omnidirectional reflectors for high photon extraction efficiency in III-nitride ultraviolet emitters,” Nanoscale 9(22), 7625–7630 (2017).
[Crossref]

Park, Y.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Prasad, S.

R. K. Mondal, V. Chatterjee, S. Prasad, and S. Pal, “Suppression of efficiency droop in AlGaN based deep UV LEDs using double side graded electron blocking layer,” Semicond. Sci. Technol. 35(5), 055031 (2020).
[Crossref]

Rass, J.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Reich, C.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Rodriguez, H.

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

Ryu, H. Y.

H. Y. Ryu, I. G. Choi, H. S. Choi, and J. I. Shim, “Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Express 6(6), 062101 (2013).
[Crossref]

Saito, A.

H. Inagaki, A. Saito, H. Sugiyama, T. Okabayashi, and S. Fujimoto, “Rapid inactivation of SARS-CoV-2 with Deep-UV LED irradiation,” Emerging Microbes Infect. 9(1), 1744–1747 (2020).
[Crossref]

Sakai, J.

T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
[Crossref]

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

Shim, J. I.

H. Y. Ryu, I. G. Choi, H. S. Choi, and J. I. Shim, “Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Express 6(6), 062101 (2013).
[Crossref]

Shin, I. S.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Shinzato, H.

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

Shmagin, I. K.

J. F. Muth, J. H. Lee, I. K. Shmagin, R. M. Kolbas, H. C. Casey, B. P. Keller, U. K. Mishra, and S. P. DenBaars, “Absorption coefficient, energy gap, exciton binding energy, and recombination lifetime of GaN obtained from transmission measurements,” Appl. Phys. Lett. 71(18), 2572–2574 (1997).
[Crossref]

Sitar, Z.

Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
[Crossref]

Soga, T.

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
[Crossref]

Sugiyama, H.

H. Inagaki, A. Saito, H. Sugiyama, T. Okabayashi, and S. Fujimoto, “Rapid inactivation of SARS-CoV-2 with Deep-UV LED irradiation,” Emerging Microbes Infect. 9(1), 1744–1747 (2020).
[Crossref]

Takagi, H.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Takano, T.

T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
[Crossref]

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

Takeda, K.

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Takeuchi, T.

T. Nakashima, K. Takeda, H. Shinzato, M. Iwaya, S. Kamiyama, T. Takeuchi, I. Akasaki, and H. Amano, “Combination of indium-tin oxide and SiO2/AlN dielectric multilayer reflective electrodes for ultraviolet-light-emitting diodes,” Jpn. J. Appl. Phys. 52(8S), 08JG07 (2013).
[Crossref]

Tashiro, T.

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

Toyoda, S.

H. Hirayama, N. Maeda, S. Fujikawa, S. Toyoda, and N. Kamata, “Recent progress and future prospects of AlGaN-based high-efficiency deep-ultraviolet light- emitting diodes,” Jpn. J. Appl. Phys. 53(10), 100209 (2014).
[Crossref]

Tsubaki, K.

T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
[Crossref]

H. Hirayama, T. Takano, J. Sakai, T. Mino, K. Tsubaki, N. Maeda, M. Jo, Y. Kanazawa, I. Ohshima, T. Matsumoto, and N. Kamata, “Realization of over 10% EQE AlGaN deep-UV LED by using transparent p-AlGaN contact layer,” Conf. Dig. - IEEE Int. Semicond. Laser Conf. 91(6), 7–8 (2016).
[Crossref]

Tsuzuki, H.

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Umeno, M.

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
[Crossref]

Vogt, P.

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

Wan, H.

H. Wan, S. Zhou, S. Lan, and C. Gui, “Light Extraction Efficiency Optimization of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes,” ECS J. Solid State Sci. Technol. 9(4), 046002 (2020).
[Crossref]

Wan, Q.

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

Wang, G.

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
[Crossref]

Wang, J.

Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).

Wang, S.

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018).
[Crossref]

Watanabe, J.

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
[Crossref]

Wernicke, T.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Weyers, M.

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

Wu, F.

Wu, R. T.

S. H. Chao, L. H. Yeh, R. T. Wu, K. Kawagishi, and S. C. Hsu, “Novel patterned sapphire substrates for enhancing the efficiency of GaN-based light-emitting diodes,” RSC Adv. 10(28), 16284–16290 (2020).
[Crossref]

Xie, J.

Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
[Crossref]

Xie, Z.

W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018).
[Crossref]

Xing, H. G.

C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018).
[Crossref]

Xu, L.

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

Yamashita, Y.

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Yan, J.

Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).

Yeh, L. H.

S. H. Chao, L. H. Yeh, R. T. Wu, K. Kawagishi, and S. C. Hsu, “Novel patterned sapphire substrates for enhancing the efficiency of GaN-based light-emitting diodes,” RSC Adv. 10(28), 16284–16290 (2020).
[Crossref]

Yoon, E.

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

Yoshida, H.

H. Tsuzuki, F. Mori, K. Takeda, T. Ichikawa, M. Iwaya, S. Kamiyama, H. Amano, I. Akasaki, H. Yoshida, M. Kuwabara, Y. Yamashita, and H. Kan, “High-performance UV emitter grown on high-crystalline-quality AlGaN underlying layer,” Phys. Status Solidi A 206(6), 1199–1204 (2009).
[Crossref]

Yu, G.

G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, and T. Jimbo, “Optical properties of wurtzite structure GaN on sapphire around fundamental absorption edge (0.78-4.77 eV) by spectroscopic ellipsometry and the optical transmission method,” Appl. Phys. Lett. 70(24), 3209–3211 (1997).
[Crossref]

Yu, X.

W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018).
[Crossref]

Yun, J.

N. Maeda, J. Yun, M. Jo, and H. Hirayama, “Enhancing the light-extraction efficiency of AlGaN deep-ultraviolet light-emitting diodes using highly reflective Ni/Mg and Rh as p-type electrodes,” Jpn. J. Appl. Phys. 57(4S), 04FH08 (2018).
[Crossref]

Zhang, J.

C. Liu, Y. K. Ooi, S. M. Islam, H. G. Xing, D. Jena, and J. Zhang, “234 nm and 246 nm AlN-Delta-GaN quantum well deep ultraviolet light-emitting diodes,” Appl. Phys. Lett. 112(1), 011101 (2018).
[Crossref]

H. Long, S. Wang, J. Dai, F. Wu, J. Zhang, J. Chen, R. Liang, Z. C. Feng, and C. Chen, “Internal strain induced significant enhancement of deep ultraviolet light extraction efficiency for AlGaN multiple quantum wells grown by MOCVD,” Opt. Express 26(2), 680 (2018).
[Crossref]

Zhang, R.

W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018).
[Crossref]

Zhang, S.

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).

Zhang, Y.

Y. Guo, Y. Zhang, J. Yan, X. Chen, S. Zhang, J. Wang, and J. Li, “Enhancement of light extraction on AlGaN-based deep-ultraviolet light-emitting diodes using a sidewall reflection method,” 2016 Int. Forum Wide Bandgap Semicond. China, IFWS 2016 - Conf. Proc. 127–130 (2017).

Zheng, Y.

W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018).
[Crossref]

Zhou, S.

H. Wan, S. Zhou, S. Lan, and C. Gui, “Light Extraction Efficiency Optimization of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes,” ECS J. Solid State Sci. Technol. 9(4), 046002 (2020).
[Crossref]

Zhou, Y.

W. Chen, Y. Zhou, X. Yu, Z. Xie, R. Zhang, and Y. Zheng, “The Effect of the Original Thickness of Ag in the Graphene-Ag Nanodots Transparent Conductive Layer on the Electrical and Optical Properties of GaN-Based UV-LEDs,” IEEE Trans. Electron Devices 65(9), 3803–3808 (2018).
[Crossref]

ACS Photonics (1)

S. Wang, J. Dai, J. Hu, S. Zhang, L. Xu, H. Long, J. Chen, Q. Wan, H. C. Kuo, and C. Chen, “Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure,” ACS Photonics 5(9), 3534–3540 (2018).
[Crossref]

Appl. Phys. Express (3)

T. Takano, T. Mino, J. Sakai, N. Noguchi, K. Tsubaki, and H. Hirayama, “Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency,” Appl. Phys. Express 10(3), 031002 (2017).
[Crossref]

Y. Kashima, N. Maeda, E. Matsuura, M. Jo, T. Iwai, T. Morita, M. Kokubo, T. Tashiro, R. Kamimura, Y. Osada, H. Takagi, and H. Hirayama, “High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer,” Appl. Phys. Express 11(1), 012101 (2018).
[Crossref]

H. Y. Ryu, I. G. Choi, H. S. Choi, and J. I. Shim, “Numerical investigation of light extraction efficiency in AlGaN deep ultraviolet light-emitting diodes,” Appl. Phys. Express 6(6), 062101 (2013).
[Crossref]

Appl. Phys. Lett. (7)

D. Lee, J. W. Lee, J. Jang, I. S. Shin, L. Jin, J. H. Park, J. Kim, J. Lee, H. S. Noh, Y. Il Kim, Y. Park, G. Do Lee, Y. Park, J. K. Kim, and E. Yoon, “Improved performance of AlGaN-based deep ultraviolet light-emitting diodes with nano-patterned AlN/sapphire substrates,” Appl. Phys. Lett. 110(19), 191103 (2017).
[Crossref]

C. Reich, M. Guttmann, M. Feneberg, T. Wernicke, F. Mehnke, C. Kuhn, J. Rass, M. Lapeyrade, S. Einfeldt, A. Knauer, V. Kueller, M. Weyers, R. Goldhahn, and M. Kneissl, “Strongly transverse-electric-polarized emission from deep ultraviolet AlGaN quantum well light emitting diodes,” Appl. Phys. Lett. 107(14), 142101 (2015).
[Crossref]

Z. Bryan, I. Bryan, J. Xie, S. Mita, Z. Sitar, and R. Collazo, “High internal quantum efficiency in AlGaN multiple quantum wells grown on bulk AlN substrates,” Appl. Phys. Lett. 106(14), 142107 (2015).
[Crossref]

N. Lobo, H. Rodriguez, A. Knauer, M. Hoppe, S. Einfeldt, P. Vogt, M. Weyers, and M. Kneissl, “Enhancement of light extraction in ultraviolet light-emitting diodes using nanopixel contact design with Al reflector,” Appl. Phys. Lett. 96(8), 081109 (2010).
[Crossref]

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Supplementary Material (1)

NameDescription
» Supplement 1       Hall data for a p-Al0.4Ga0.6N/Al0.67Ga0.33N superlattice layer. The hole concentration in this p-AlGaN superlattice layer is 3.7×1018 cm-3 at room temperature.

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Figures (5)

Fig. 1.
Fig. 1. Schematic structures of DUV-LEDs with (a) Ag nanodots/Al electrodes and (b) Ni/Au electrodes.
Fig. 2.
Fig. 2. Morphology evolution of Ag under different annealing conditions: (a) 300 ℃ for 3 minutes, (b) 400 ℃ for 3 minutes, and (c) 500 ℃ for 1 minute. (d) Transmittance spectra of Ag nanodots on sapphire under different annealing conditions.
Fig. 3.
Fig. 3. (a) Cross-sectional TEM image, (b) AFM image of the LED with thin p-GaN. (c) Transmittance of the p-AlGaN superlattice. (d) Reflectivity of the Ag nanodots/Al complex electrodes.
Fig. 4.
Fig. 4. (a) Comparison of lateral I-V characteristics of Ni/Au contact and Ag nanodots/Al complex electrodes on p-GaN. (b) The I-V characteristics of DUV-LED structures A and B.
Fig. 5.
Fig. 5. (a) The EL spectra of structures A and B at 100 mA. (b) The FWHM and wavelength, and (c) The EQE and LOP of structures A and B under different injection current.