Open Access
Add to BibSonomy
Abstract
In this paper, α-Ga2O3 nanorod arrays (NRAs) with preferential growth along the (110) direction were successfully prepared on the FTO substrate by the water bath method. With the help of a scanning electron microscope (SEM), X-ray diffractometer (XRD), and Raman spectrometer (Raman), the crystal structure and morphology characteristics of α-Ga2O3 NRAs were studied. On this basis, a photoelectrochemical (PEC) solar-blind ultraviolet photodetector based on the α-Ga2O3 NRAs was fabricated, and the photoelectric performance of the device was analyzed in detail through the PEC test system, and the working mechanism of the device was further discussed. The results show that the prepared α-Ga2O3 NRAs have good crystal quality which is closely arranged on the substrate and a quadrangular prism shape from the top view. The constructed α-Ga2O3 NRAs PEC photodetector shows typical solar-blind ultraviolet response characteristics and stable self-powered ability. Meanwhile, the device exhibited a high photo-dark current ratio (PDCR), responsivity (R) and detectivity (D*) of 1.01×103, 11.34 mA/W and 2.68×1011 Jones, respectively, as well as superior wavelength selectivity and fast response. This work confirms that α-Ga2O3 NRAs prepared by the water bath method have potential application prospects in highly sensitive and fast response PEC self-powered solar-blind ultraviolet photodetectors.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
According to the wavelength distribution, the solar spectrum is simply divided into three bands: visible, infrared and ultraviolet. The ultraviolet band can be further divided into long-wave (UVA: 315∼400 nm), medium-wave (UVB: 280∼315 nm) and short-wave (UVC: 200∼280 nm) [1]. The UVC radiation from the Sun can be absorbed and scattered by the ozone layer and stratosphere during the propagation process. Therefore, the natural UVC radiation cannot be detected on the earth's surface, which is also defined as the solar blind region [2]. The very low background noise brings many possibilities for the application of ultraviolet rays, such as detection (ozone layer hole detection [3], flame detection [3,4], corona detection [5], missile plume detection [6], etc.), UV communication [7], UV imaging [8], biomedicine [6], etc.
At present, the ultra-wide bandgap semiconductor materials, represented by AlGaN [9], MgZnO [10], ZnGaO [11], AlN [12], BN [13], diamond [14], Ga2O3 [15] and so on, have become hot spots for the preparation of solar-blind ultraviolet photodetectors (PDs). However, most materials are more or less subject to certain restrictions, such as high alloying causing reduced crystal quality and/or phase segregation [16], and larger bandgap leading to limited detection in solar blind region [17]. In contrast, the band gap of Ga2O3 is usually between 4.6 eV to 5.2 eV and can be adjusted by doping approach, which further meets well with the UVC wavelength range [18]. In addition, Ga2O3 also has a higher electron breakdown field and better thermal/chemical stabilities [19]. All the above features facilitate Ga2O3 to become the optimal material for the fabrication of solar-blind ultraviolet photodetectors [20]. As is well-known, Ga2O3 has six crystal structures of α, β, γ, ɛ, κ and δ [21]. Among them, α-Ga2O3 belongs to the trigonal crystal system and the corresponding space group is R-3c [22]. In 2010, Yu et al. successfully prepared Eu doped α-Ga2O3 nanoparticles by the hydrothermal method [23]. In 2011, Muruganandham et al. reported a method to synthesized α-GaOOH and α-Ga2O3 through a self-assembly approach [24]. Currently, α-Ga2O3 has been used to develop solar-blind ultraviolet photodetectors [25–27].
More recently, self-powered photodetectors have gradually attracted attention because they do not require an external power supply and are convenient for miniaturization and integration. At present, self-powered photodetectors based on Ga2O3 mainly include pn junctions [28], Schottky junctions [29], heterojunctions [30] and photoelectrochemical (PEC) photodetectors [31]. Ga2O3 is a typical n-type semiconductor, while the matched p-type Ga2O3 is difficult to obtain. Most of heterojunction or Schottky photodetectors have large lattice mismatches with Ga2O3, and a complex hierarchical structure is needed to maintain high performance [32,33]. PEC-type optoelectronic devices have outstanding advantages such as simple process, fast response and strong stability, so it is expected to realize the practical application of self-powered ultraviolet photodetectors [31]. Very recently, PEC self-powered solar-blind ultraviolet photodetectors based on α-Ga2O3 have been developed. In 2019, Zhang et al. [34] reported that a novel PEC self-powered detector using a newly designed counter electrode as the light-receiving surface is applied to a hydrothermally synthesized α-Ga2O3 nanorod arrays (NRAs) to realize the detection of solar-blind ultraviolet light. At the same time, He et al. [35] used a similar process to prepare PEC-type self-powered solar-blind ultraviolet photodetector based on α-Ga2O3 NRAs. It is demonstrated that the vertical structure of the nanoarrays provides a channel for carrier transmission in α-Ga2O3, and the NRAs with a large specific surface area has a light trapping effect, which can significantly increase the light absorption rate [36]. Although α-Ga2O3 NRAs could be can be prepared by a hydrothermal method, it often requires high temperature/high pressure conditions and even a seed layer [37]. Compared with the hydrothermal method, the water bath method does not require high temperature/high pressure conditions, and has the advantages of low cost, simpler process and faster growth rate, and so on [38].
Herein, we directly synthesized α-Ga2O3 nanorod arrays through the water bath method without seed layer and constructed a novel photoelectrochemical-type self-powered solar-blind ultraviolet photodetector. The corresponding photoelectric characteristics and related mechanisms have been investigated systematically. The results show that the device has typical solar-blind ultraviolet response and stable self-powered characteristics.
2. Experiment details
2.1 Material synthesis and characterization
The α-Ga2O3 nanorod arrays (NRAs) are directly prepared on the FTO substrate by the water bath method and the post-annealing process. The detailed preparation steps are shown in Fig. 1(a). First, the FTO substrate is ultrasonically treated with alcohol, acetone and deionized water for 10 minutes in sequence, and then the cleaned FTO is stored in alcohol for later use. A 0.5 mol/L Ga(NO3)3 solution (gallium nitrate (III) hydrate 99.9%) is prepared as a water bath reaction solution. Use plastic clips to suspend the dried FTO in the reagent bottle that contains the reaction solution, then place the reagent bottle in a water bath and set the reaction temperature to 100 °C. After 12 hours of reaction, GaOOH nanorods are obtained and further wash and dry. Finally, GaOOH nanorods are annealed at 400 °C for 2 h to realize the conversion from GaOOH nanorods to α-Ga2O3 nanorod arrays under vacuum conditions. The FEI Inspect F50 field emission scanning electron microscope (SEM) was used to characterize the morphology of the sample. The structural characteristics of sample were analyzed by X-ray diffraction (Cu Kα1 radiation, λ=1.5406 Å) and Raman test system (Horiba HR Evolution, 532 nm).
Fig. 1. Schematic diagram of the preparation process (a) and device packaging (b) of the α-Ga2O3 nanorod array.
2.2 Device fabrication and measurements
In order to better determine the photosensitive area of the photoelectrochemical test and improve the corresponding stability, we packaged the sample in this work. Figure 1(b) is the schematic diagram of device packaging processes. Before packaging, 1/3 of the sample on the surface of the FTO should be scraped off to ensure the conductivity between electrode and substrate. Then, paint conductive silver is pasted on the pre-treated area and fixed one end of the copper wire (the ends of the copper wire have been pre-treated to be flat), and the calibration ring with inner diameter of 6 mm is fixed in the center of the sample. Finally, the substrate, calibration ring and copper wire are wrapped with opaque epoxy resin AB glue, and placed in a vacuum environment for curing. The calibration part is the photosensitive area of the device. After that, we use CHI440C electrochemical system and self-assembled electrolytic cell to test the photoelectrochemical performance at room temperature (RT). The working electrode is α-Ga2O3 nanorod arrays with a photosensitive area of about 0.28 cm2, the counter electrode is a platinum sheet, and the reference electrode is saturated calomel. The electrolyte is a 0.5 mol/L Na2SO4 solution. The light source is provided by a UVLS-28 EL ultraviolet lamp (254 nm and 365 nm).
3. Results and discussions
Figure 2(a) shows the XRD diffraction pattern of α-Ga2O3 nanorod arrays/FTO sample grown through the water bath method. It can be seen from the figure that in addition to the characteristic diffraction peaks caused by the FTO substrate, two additional diffractions peaks are also observed (36.8° and 64.8°) that correspond to the (110) and (300) planes of rhombohedral (α-phase) Ga2O3 (JCPDS card number: 06-0503) [31], respectively. The XRD results show that α-Ga2O3 with preferential growth along the (110) direction has been successfully prepared [31]. Besides, Raman testing was implemented to further determine the crystal structure of the sample. As shown in Fig. 2(b), five characteristic Raman peaks near P1 (217 cm-1), P2 (289 cm-1), P3 (431 cm-1), P4 (572 cm-1) and P5 (692 cm-1) are observed that belong to the α-Ga2O3 crystal with R3c symmetrical corundum structure [39]. This result further confirms that the prepared the successful synthesis of α-Ga2O3. In the Raman spectrum, different peak ranges correspond to different molecular vibration modes of α-Ga2O3, and the high-frequency peaks exceeding 600 cm-1 correspond to the v1 symmetrical pull of GaO4. The Raman movement range from 300 to 600 cm-1 is caused by the symmetrical tensile vibration of the GaO6 octahedron, while the low-frequency peaks below 200 cm-1 are attributed to the O-Ga-O bending vibration of the GaO6 octahedron [40]. Figure 2(c) and (d) shows the SEM image of the α-Ga2O3 NRAs. Figure 2(c) clearly exhibits that α-Ga2O3 nanorods with a length of about 2 µm and a diameter of 200 nm are arranged tightly and vertically on the FTO substrate. The SEM top view in Fig. 2(d) shows that the top of a single α-Ga2O3 nanorod is in the shape of a quadrangle column, and the nanorods are closely arranged.
Fig. 2. The crystal structure and surface morphology of α-Ga2O3 nanorod arrays grown on the FTO substrate: (a) XRD diffraction pattern; (b) Raman scattering pattern; (c) cross-sectional SEM image; (d) top-view SEM image.
In order to explore the performance of the photoelectrochemical (PEC) type solar-blind ultraviolet photodetector based on the α-Ga2O3 nanorod arrays, we used a three-electrode system to perform photoelectrochemical tests on the packaged sample. Figure 3(a) shows I-V curves of a PEC-type ultraviolet photodetector based on α-Ga2O3 NRAs under dark, 365 nm and 254 nm illumination with various light intensities. In the dark, the device exhibits typical rectification characteristics, which is attributed to the band bending of the α-Ga2O3 nanorod arrays at the solid-liquid interface [35]. Under 365 nm illumination, the photocurrent of the device is very close to the dark current. Obviously, the device exhibits a larger photocurrent under 254 nm illumination and the photocurrent gradually increases with the increase of light intensity, indicating that the device has light intensity-dependent characteristics. Specially, with the increase of the 254 nm light intensity, the photocurrent of the device is increased linearly under the bias of 0 V, as shown in Fig. 3(b). The noticeable photocurrent signal and low dark current at zero bias clearly demonstrate the self-powered capability, meaning that the PEC-type solar-blind ultraviolet photodetector based on the α-Ga2O3 nanorod arrays can work without external power supply.
Fig. 3. (a) The linear sweep voltammetry (LSV) curve of a photoelectrochemical ultraviolet photodetector based on α-Ga2O3 nanorod arrays under dark state, 365 nm and 254 nm illumination; (b) The functional relationship between light intensity and photocurrent under zero bias; (c) I-t curves under different light intensities at 0 V bias; (d) The enlarged I-t curve at 0 V bias.
Figure 3(c) is the I-t characteristic curve of the PEC-type solar-blind ultraviolet photodetector based on the α-Ga2O3 nanorod arrays under zero bias. It can be concluded from the figure that the device has almost no response to 365 nm light. The solar-blind deep ultraviolet light response at 254 nm is obvious, indicating that the device has considerable selectivity. At the same time, the device has good stability when the on/off period is 10 s and there is an obvious light intensity dependence. The photo-dark current ratio (PDCR) is defined as the ratio of the on-state current to the off-state current of the device. Combining the photocurrent and dark current, it can be calculated that when the light intensity is 0.5 mW/cm2, the ratio of light to dark current under zero bias is as high as 1.01×103. Responsivity (R) is also an important parameter that characterizes the photodetector's ability to convert incident light energy to electrical signals, and the expression is [41]:
in which ΔI = Ip (photocurrent)-Id (dark current), Pinc is the 254 nm light intensity of 0.5 mW/cm2 and S is the effective illumination area of the device (∼ 0.28 cm2). It is calculated that the responsivity of device is 11.34 mA/W. Besides, the photoresponse rejection ratio (R254/R365) is the ratio of the responsivity between 254 nm and 365 nm. The value of R254/R365 is 207.8 when the light intensity is 0.5 mW/cm2, indicating that the device has a remarkable selectivity. The detectivity (D*) is another important parameter for evaluating the ability of the photodetector to detect weak signals. The specific formula is as follows [42]: where, e is the electronic charge. Under zero bias (0.5 mW/cm2), the D* of PEC-type solar-blind ultraviolet photodetector reaches 2.68×1011 Jones. The external quantum efficiency (EQE) is defined as the number of electrons detected per incident photon, which can evaluate the working efficiency of the device. The formula is defined as [43]: where, h is the Planck’s constant, c is the light speed, λ is the wavelength of DUV light. The calculated EQE of the device is 5.54%. Usually, the rise time (τr) of device is defined as the time of the current to increase from 10% of the peak value to 90%, and the decay time (τd) is defined as the time of the current decreasing from 90% of the peak value to 10%. Figure 3(d) shows the response time of the device under zero bias (0.5 mW/cm2), the response time τr/τd is calculated to be 1.51 s/0.18 s, respectively. Table 1 compares this work with the PEC-type self-powered solar-blind ultraviolet photodetector based on Ga2O3 nanomaterials in recent years. Overall, the ultrahigh PDCR, high R, D*, EQE, superior wavelength selectivity and fast response suggest that the PEC-type self-powered ultraviolet photodetector based on the α-Ga2O3 NRAs fabricated by water bath method is sensitive in the solar-blind spectrum.
Table 1. Performance comparison of the photoelectrochemical self-powered solar-blind ultraviolet photodetectors based on Ga2O3 nanomaterials.
Figure 4 shows the self-powered mechanism of the PEC-type solar-blind ultraviolet photodetector based on the α-Ga2O3 nanorod arrays. Since the Fermi energy level of α-Ga2O3 is higher than the redox energy level of the Na2SO4 electrolyte, the charge distribution difference between two is formed. When the α-Ga2O3 NRAs is in contact with the electrolyte, the energy band of the α-Ga2O3 bends upwards, thereby forming a built-in electric field from α-Ga2O3 to the interface [35]. When a deep ultraviolet light irritates the α-Ga2O3 NRAs surface, a large number of photogenerated electrons will transfer from the valence band to the conduction band, leaving holes in the valence band while the electrons on the conduction band gradually accumulate. The electrons on the conduction band move to the FTO under the driving force of built-in electric field, and finally collect on the counter electrode through the external circuit [42]. The holes accumulated in the valence band first oxidize OH- in the electrolyte to OH* (OH-+h+=OH*), while the generated OH* are reduced to OH- (OH*+e-=OH-). In short, the reaction is generally through the redox of OH- and OH* in the electrolyte and realize the conduction of the circuit, and finally exhibits self-powered characteristics.
Fig. 4. Mechanism diagram of photoelectrochemical self-powered ultraviolet photodetector based on α-Ga2O3 nanorod arrays.
4. Conclusion
In this paper, the α-Ga2O3 NRAs without the need for a seed layer were successfully prepared on the FTO substrate by the water bath method and post-annealing process. The fabricated novel photoelectrochemical (PEC) photodetector based on the α-Ga2O3 NRAs has typical solar-blind ultraviolet response and stable self-powered characteristics. The device exhibited high PDCR, R and D* of 1.01×103, 11.34 mA/W and 2.68×1011 Jones, respectively, as well as superior wavelength selectivity and fast response. Our results confirm the high-performance PEC solar blind photodetector based on α-Ga2O3 NRAs prepared by the water bath method with low power consumption are promising candidates for the future solar-blind photodetection.
Funding
National Natural Science Foundation of China (11904041); Natural Science Foundation of Chongqing (cstc2019jcyj-msxmX0237, cstc2020jcyj-msxmX0533, cstc2020jcyj-msxmX0557); Science and Technology Research Project of Chongqing Education Committee (KJ1703042, KJQN201800501, KJQN201900542, KJQN20200051); College Students Innovation and Entrepreneurship Training Program of Chongqing City (S202010637018).
Disclosures
The authors declare that they have no conflict of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. J. Pearton S, J. Yang, P. H. Cary IV, F. Ren, J. Kim, J. Tadjer M, and A. Mastro M, “A review of Ga2O3 materials, processing, and devices,” Appl. Phys. Rev. 5(1), 011301 (2018). [CrossRef]
2. X. Chen, F. Ren, S. Gu, and J. Ye, “Review of gallium-oxide-based solar-blind ultraviolet photodetectors,” Photonics Res. 7(4), 381–415 (2019). [CrossRef]
3. H. Chen, K. Liu, L. Hu, A. Al-Ghamdi A, and X. Fang, “New concept ultraviolet photodetectors,” Mater. Today 18(9), 493–502 (2015). [CrossRef]
4. P. Li, H. Shi, K. Chen, D. Guo, W. Cui, Y. Zhi, S. Wang, Z. Wu, Z. Chen, and W. Tang, “Construction of GaN/Ga2O3 p–n junction for an extremely high responsivity self-powered UV photodetector,” J. Mater. Chem. C 5(40), 10562–10570 (2017). [CrossRef]
5. P. Fan, K. Chettiar U, L. Cao, F. Afshinmanesh, N. Engheta, and L. Brongersma M, “An invisible metal–semiconductor photodetector,” Nat. Photonics 6(6), 380–385 (2012). [CrossRef]
6. Z. Wu, L. Jiao, X. Wang, D. Guo, W. Li, L. Li, F. Huang, and W. Tang, “A self-powered deep-ultraviolet photodetector based on an epitaxial Ga2O3/Ga:ZnO heterojunction,” J. Mater. Chem. C 5(34), 8688–8693 (2017). [CrossRef]
7. S. Assefa, F. Xia, and A. Vlasov Y, “Reinventing germanium avalanche photodetector for nanophotonic on-chip optical interconnects,” Nature 464(7285), 80–84 (2010). [CrossRef]
8. A. Kalra, S. Vura, S. Rathkanthiwar, R. Muralidharan, S. Raghavan, and N. Nath D, “Demonstration of high-responsivity epitaxial β-Ga2O3/GaN metal–heterojunction-metal broadband UV-A/UV-C detector,” Appl. Phys. Express 11(6), 064101 (2018). [CrossRef]
9. R. McClintock, A. Yasan, K. Mayes, D. Shiell, R. Darvish S, P. Kung, and M. Razeghi, “High quantum efficiency AlGaN solar-blind pin photodiodes,” Appl. Phys. Lett. 84(8), 1248–1250 (2004). [CrossRef]
10. S. Jheng J, K. Wang C, Z. Chiou Y, P. Chang S, and J. Chang S, “MgZnO/SiO2/ZnO metal–semiconductor–metal dual-band UVA and UVB photodetector with different MgZnO thicknesses by RF magnetron sputter,” Jpn. J. Appl. Phys. 59(SD), SDDF04 (2020). [CrossRef]
11. H. Horng R, H. Huang P, S. Li Y, G. Tarntair F, and S. Tan C, “Reliability study on deep-ultraviolet photodetectors based on ZnGa2O4 epilayers grown by MOCVD,” Appl. Surf. Sci. 555, 149657 (2021). [CrossRef]
12. A. Knigge, M. Brendel, F. Brunner, S. Einfeldt, A. Knauer, and V. Kueller, “Weyers M. AlGaN photodetectors for the UV-C spectral region on planar and epitaxial laterally overgrown AlN/sapphire templates,” Phys. Status Solidi C 10(3), 294–297 (2013). [CrossRef]
13. H. Liu, J. Meng, X. Zhang, Y. Chen, Z. Yin, D. Wang, Y. Wang, J. You, M. Guo, and P. Jin, “High-performance deep ultraviolet photodetectors based on few-layer hexagonal boron nitride,” Nanoscale 10(12), 5559–5565 (2018). [CrossRef]
14. T. He, Y. Zhao, X. Zhang, W. Lin, K. Fu, C. Sun, and B. Zhang, “Solar-blind ultraviolet photodetector based on graphene/vertical Ga2O3 nanowire array heterojunction,” Nanophotonics 7(9), 1557–1562 (2018). [CrossRef]
15. J. Lu Y, N. Lin C, and X. Shan C, “Optoelectronic diamond: growth, properties, and photodetection applications,” Adv. Opt. Mater. 6, 1800359 (2018). [CrossRef]
16. M. Fan M, W. Liu K, X. Chen, X. Wang, Z. Zhang Z, H. Li B, and Z. Shen D, “Mechanism of excellent photoelectric characteristics in mixed-phase ZnMgO ultraviolet photodetectors with single cutoff wavelength,” ACS Appl. Mater. Interfaces 7(37), 20600–20606 (2015). [CrossRef]
17. C. Chen Y, J. Lu Y, N. Lin C, Z. Tian Y, J. Gao C, L. Dong, and X. Shan C, “Self-powered diamond/β-Ga2O3 photodetectors for solar-blind imaging,” J. Mater. Chem. C 6(21), 5727–5732 (2018). [CrossRef]
18. Y. Zhang, J. Yan, Q. Li, C. Qu, L. Zhang, and W. Xie, “Optical and structural properties of Cu-doped β-Ga2O3 films,” Mater. Sci. Eng., B 176(11), 846–849 (2011). [CrossRef]
19. P. Rex J, K. Yam F, and H. San Lim, “The influence of deposition temperature on the structural, morphological and optical properties of micro-size structures of beta-Ga2O3,” Results Phys. 14, 102475 (2019). [CrossRef]
20. Q. Zheng X, Y. Xie, J. Lee, Z. Jia, X. Tao, and X. L. Feng P, “Beta gallium oxide (β-Ga2O3) nanoelectromechanical transducer for dual-modality solar-blind ultraviolet light detection,” APL Mater. 7(2), 022523 (2019). [CrossRef]
21. V. Gottschalch, S. Merker, S. Blaurock, M. Kneiß, U. Teschner, M. Grundmann, and H. Krautscheid, “Heteroepitaxial growth of α-, β-, γ-and κ-Ga2O3 phases by metalorganic vapor phase epitaxy,” J. Cryst. Growth 510, 76–84 (2019). [CrossRef]
22. Y. Xu, C. Zhang, Y. Cheng, Z. Li, N. Cheng Y, Q. Feng, D. Chen, J. Zhang, and Y. Hao, “Influence of carrier gases on the quality of epitaxial corundum-structured α-Ga2O3 films grown by mist chemical vapor deposition method,” Materials 12(22), 3670 (2019). [CrossRef]
23. U. A. N. Yu Q, Q. Liu S, L. Huang K, A. N. G. Dong F, Y. Zhang X, and W. Hou H, “Hydrothermal synthesis and characterization of Eu-doped GaOOH/α-Ga2O3/β-Ga2O3 nanoparticles,” Trans. Nonferrous Met. Soc. China 20(8), 1458–1462 (2010). [CrossRef]
24. M. Muruganandham, R. Amutha, S. A. Wahed M, B. Ahmmad, Y. Kuroda, P. Suri R, J. Wu J, and E. Sillanpaa M, “Controlled fabrication of α-GaOOH and α-Ga2O3 self-assembly and its superior photocatalytic activity,” J. Phys. Chem. C 116(1), 44–53 (2012). [CrossRef]
25. X. Chen, Y. Xu, D. Zhou, S. Yang, F. Ren F, H. Lu, K. Tang, S. Gu, R. Zhang, Y. Zheng, and J. Ye, “Solar-blind photodetector with high avalanche gains and bias-tunable detecting functionality based on metastable phase α-Ga2O3/ZnO isotype heterostructures,” ACS Appl. Mater. Interfaces 9(42), 36997–37005 (2017). [CrossRef]
26. G. Qiao, Q. Cai, T. Ma, J. Wang, X. Chen, Y. Xu, Z. Shao, J. Ye, and D. Chen, “Nanoplasmonically enhanced high-performance metastable phase α-Ga2O3 solar-blind photodetectors,” ACS Appl. Mater. Interfaces 11(43), 40283–40289 (2019). [CrossRef]
27. J. Moloney, O. Tesh, M. Singh, W. Roberts J, C. Jarman J, C. Lee L, N. Huq T, J. Brister, S. Karboyan, and C. Massabuau F, “Atomic layer deposited α-Ga2O3 solar-blind photodetectors,” J. Phys. D: Appl. Phys. 52(47), 475101 (2019). [CrossRef]
28. D. Guo, Y. Su, H. Shi, P. Li, N. Zhao, J. Ye, S. Wang, A. Liu, Z. Chen, C. Li, and W. Tang, “Self-powered ultraviolet photodetector with superhigh photoresponsivity (3.05 A/W) based on the GaN/Sn: Ga2O3 pn junction,” ACS Nano 12(12), 12827–12835 (2018). [CrossRef]
29. J. Yu, J. Lou, Z. Wang, S. Ji, J. Chen, M. Yu, B. Peng, Y. Hu, L. Yuan, Y. Zhang, and R. Jia, “Surface modification of β-Ga2O3 layer using pt nanoparticles for improved deep UV photodetector performance,” J. Alloys Compd. 872, 159508 (2021). [CrossRef]
30. H. Wang, H. Chen, L. Li, Y. Wang, L. Su, W. Bian, B. Li, and X. Fang, “High responsivity and high rejection ratio of self-powered solar-blind ultraviolet photodetector based on PEDOT: PSS/β-Ga2O3 organic/inorganic p–n junction,” J. Phys. Chem. Lett. 10(21), 6850–6856 (2019). [CrossRef]
31. J. Zhang, S. Jiao, D. Wang, S. Gao, J. Wang, and L. Zhao, “Nano tree-like branched structure with α-Ga2O3 covered by γ-Al2O3 for highly efficient detection of solar-blind ultraviolet light using self-powered photoelectrochemical method,” Appl. Surf. Sci. 541, 148380 (2021). [CrossRef]
32. C. Yang, H. Liang, Z. Zhang, X. Xia, P. Tao, Y. Chen, H. Zhang, R. Shen, Y. Luo, and G. Du, “Self-powered SBD solar-blind photodetector fabricated on the single crystal of β-Ga2O3,” RSC Adv. 8(12), 6341–6345 (2018). [CrossRef]
33. J. Yu, L. Dong, B. Peng, L. Yuan, Y. Huang, L. Zhang, Y. Zhang, and R. Jia, “Self-powered photodetectors based on β-Ga2O3/4H–SiC heterojunction with ultrahigh current on/off ratio and fast response,” J. Alloys Compd. 821, 153532 (2020). [CrossRef]
34. J. Zhang, S. Jiao, D. Wang, S. Ni, S. Gao, and J. Wang, “Solar-blind ultraviolet photodetection of an α-Ga2O3 nanorod array based on photoelectrochemical self-powered detectors with a simple, newly-designed structure,” J. Mater. Chem. C 7(23), 6867–6871 (2019). [CrossRef]
35. K. Chen, S. Wang, C. He, H. Zhu, H. Zhao, D. Guo, Z. Chen, J. Shen, P. Li, A. Liu, C. Li, F. Wu, and W. Tang, “Photoelectrochemical self-powered solar-blind photodetectors based on Ga2O3 nanorod array/electrolyte solid/liquid heterojunctions with a large separation interface of photogenerated carriers,” ACS Appl. Nano Mater. 2(10), 6169–6177 (2019). [CrossRef]
36. Q. Hu, J. Wang, Y. Cao, Y. Zhao, and D. Li, “Light-trapping enhancement based on Ga2O3 nano-islands coated glass substrate,” Sol. Energy 86(3), 855–859 (2012). [CrossRef]
37. H. J. Bae, T. H. Yoo, Y. Yoon, I. G. Lee, J. P. Kim, B. J. Cho, and W. S. Hwang, “High-Aspect Ratio β-Ga2O3 Nanorods via Hydrothermal Synthesis,” Nanomaterials 8(8), 594 (2018). [CrossRef]
38. S. Yu, G. Zhang, D. Carloni, and Y. Wu, “Fabrication, microstructure and optical properties of Ga2O3 transparent ceramics,” Ceram. Int. 46(13), 21757–21761 (2020). [CrossRef]
39. T Ma, X Chen, F Ren, S Zhu, S Gu, R Zhang, Y Zheng, and J Ye, “Heteroepitaxial growth of thick α-Ga2O3 film on sapphire (0001) by MIST-CVD technique,” J. Semicond. 40(1), 012804 (2019). [CrossRef]
40. J. Wang, L. Ye, X. Wang, H. Zhang, L. Li, C. Kong, and W. Li, “High transmittance β-Ga2O3 thin films deposited by magnetron sputtering and post-annealing for solar-blind ultraviolet photodetector,” J. Alloys Compd. 803, 9–15 (2019). [CrossRef]
41. R. Zhuo, D. Wu, Y. Wang, E. Wu, C. Jia, Z. Shi, T. Xu, Y. Tian, and X. Li, “A self-powered solar-blind photodetector based on a MoS2/β-Ga2O3 heterojunction,” J. Mater. Chem. C 6(41), 10982–10986 (2018). [CrossRef]
42. Y. Wang, W. Cui, J. Yu, Y. Zhi, H. Li, Z. Hu, X. Sang, E. Guo, T. Tang, and Z. Wu, “One-step growth of Amorphous/Crystalline Ga2O3 phase junctions for high-performance solar-blind photodetection,” ACS Appl. Mater. Interfaces 11(49), 45922–45929 (2019). [CrossRef]
43. W. Zheng, F. Huang, R. Zheng, and H. Wu, “Low-dimensional structure vacuum-ultraviolet-sensitive (λ 200 nm) photodetector with fast-response speed based on high-quality AlN micro/nanowire,” Adv. Mater. 27(26), 3921–3927 (2015). [CrossRef]
44. C. He, D. Guo, K. Chen, S. Wang, J. Shen, N. Zhao, A. Liu, Y. Zheng, P. Li, Z. Wu, C. Li, F. Wu, and W. Tang, “α-Ga2O3 nanorod array–Cu2O microsphere p–n junctions for self-powered spectrum-distinguishable photodetectors,” ACS Appl. Nano Mater. 2(7), 4095–4103 (2019). [CrossRef]
45. Y. Chen, K. Zhang, X. Yang, X. Chen, J. Sun, Q. Zhao, K. Li, and C. Shan, “Solar-blind photodetectors based on MXenes–β-Ga2O3 Schottky junctions,” J. Phys. D: Appl. Phys. 53(48), 484001 (2020). [CrossRef]
46. Z. Liu, X. Wang, Y. Liu, D. Guo, S. Li, Z. Yan, C. Tan, W. Li, P. Li, and W. Tang, “A high-performance ultraviolet solar-blind photodetector based on a β-Ga2O3 Schottky photodiode,” J. Mater. Chem. C 7(44), 13920–13929 (2019). [CrossRef]
47. B. Zhao, F. Wang, H. Chen, L. Zheng, L. Su, D. Zhao, and X. Fang, “An ultrahigh responsivity (9.7 mA W− 1) self-powered solar-blind photodetector based on individual ZnO–Ga2O3 heterostructures,” Adv. Funct. Mater. 27, 1700264 (2017). [CrossRef]
48. J. Yu, M. Yu, Z. Wang, L. Yuan, Y. Huang, L. Zhang, Y. Zhang, and R. Jia, “Improved photoresponse performance of self-powered β-Ga2O3/NiO heterojunction UV photodetector by surface plasmonic effect of Pt nanoparticles,” IEEE Trans. Electron Devices 67(8), 3199–3204 (2020). [CrossRef]
