Abstract

Indium oxide (In2O3) films grown by thermal oxidation on MgO substrates were optically excited by femtosecond laser pulses having photon energy lower than the In2O3 bandgap. Terahertz (THz) pulse emission was observed using time domain spectroscopy. Results show that THz emission saturates at an excitation fluence of ~400 nJ/cm2. Even as two-photon absorption has been excluded, the actual emission mechanism has yet to be confirmed but is currently attributed to carriers due to weak absorption from defect levels that are driven by a strain field at the interface of the substrate and the grown film.

©2012 Optical Society of America

1. Introduction

The search for new and novel semiconductor materials as terahertz (THz) surface emitters is a vital aspect of THz research [1]. In particular, wide-bandgap semiconductors are of interest due to their inherent transparency in the near-infrared (NIR) and visible regions. Highly transparent materials over a broad spectral region are crucial components in THz integrated optics design [2]. It is also worth noting that wide bandgap semiconductors likewise promise to be viable THz photoconductive antennas (PCA’s) as they can be operated at higher bias fields for improved signal-to-noise ratio [3]. Their major drawback, however, is that they require intense short-wavelength excitation sources and these types of excitation sources are not in abundance at this time primarily due to prohibitive costs.

Indium oxide (In2O3) is a wide-bandgap n-type metal oxide semiconductor with high optical transparency in the visible region [47]. The applications of In2O3 range from transparent electronics, to light-emitting diodes (LEDs), photodetectors, solar cells, flat panel displays, thin film transistors, and even high sensitivity detection of various gases and biomedical applications [49]. Recently, the actual energy bandgap of this semiconductor has been extensively debated on due to the emergence of growth techniques that are capable of producing high quality defect-less single-crystal In2O3 films that yield varying bandgap values. Oxygen plasma assisted MBE-grown In2O3 films on Yttria-stabilized Zirconia (YSZ) substrates have recorded a bandgap of about 2.9 eV (427 nm), much lower than the well known value of 3.75eV- 4eV [10,11]. This direct energy gap is suggested to be the only bandgap corresponding to cubic In2O3 in contrast to previous reports [10,12]. The surface electronic investigation on cubic In2O3 also reveals preference of electron accumulation. It has been found that charge accumulates along the (001) and (111) planes of its lattice, hence having electronic characteristic similar to InN and InAs [13,14]. As these two materials are considered to be intense semiconductor surface THz emitters, these previous reports suggest the viability of In2O3 as a THz emission source, as well [10,11]. Thermal oxidation techniques have previously demonstrated the growth of In2O3 films [4]. Moreover, Sieber, et. al., reported the growth of polycrystalline In2O3 on magnesium oxide (MgO) [15] despite a large lattice mismatch. The In2O3 lattice constant along the a-axis is around 10.12 Å while MgO has 4.21 Å.

In this work, we experimentally demonstrate THz emission from photo-excited In2O3 films on single crystal MgO (100) prepared by thermal oxidation. The MgO substrate is so chosen due of its excellent transmission properties both in the optical and THz-frequency regimes, high-melting temperature, and low electrical conductivity [16]. Results show that even at an excitation photon energy which is lower than the bandgap, the In2O3 films exhibited THz emission. Additionally, the dependence of the THz emission on the oxidation temperature and excitation fluence was also studied in an attempt to explain the underlying THz radiation mechanism.

2. Experiment

The In2O3 thin films were formed via thermal oxidation of Indium films deposited on single crystal MgO (001) substrates. The MgO substrates were primarily cleaned, rinsed and blow-dried. Indium metal with 99.999% purity was then thermally evaporated on the substrates at a rate of 6Å/s in a 3x10−5-Torr vacuum environment. A quartz crystal sensor indicated the indium film thickness to be ~1500Å. The samples were then oxidized in ambient air at three different temperatures (350°C, 450°C, and 550°C). Initial thin film characterization was carried out via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The THz emission was measured using standard THz-time domain spectroscopy (THz-TDS) methods. The optical excitation was provided for by a p-polarized mode-locked Ti:Sapphire laser delivering ~80 femtosecond pulses at a central wavelength of 800 nm with a repetition rate of 82 MHz. The samples were excited at a 45ο incidence with an average pump power of 150 mW, loosely focused to a beam spot size of ~1 mm. The THz radiation was collected in the specular reflection direction and focused to the detector using appropriate off-axis paraboloid mirrors. The THz temporal waveforms were detected by a Hamamatsu LT-GaAs dipole-type photoconductive antenna, switched by a variable time-delayed 20 mW optical pulse.

3. Results and discussion

As shown in Fig. 1(a) , the SEM images of the three In2O3/MgO films, exhibited grain structures. At a higher magnification of x1200 (inset), these grains are shown to have similar size distributions and shapes, regardless of the oxidation temperature. A more quantitative discussion is offered by the XRD data in Fig. 1(b). The most intense peak is the (002) peak associated with the MgO substrate. The other observed features shows XRD peaks at 30.26°, 35.14°, 43.98° and 77.46° corresponding to (222), (400), (422), and (820) planes (from JCPDS #06-416). The peaks are indexed against a cubic In2O3 unit cell with lattice parameter a = 10.1 Å. This observation is consistent with the previous studies done on the thermal oxidation of Indium films on silicon and glass substrates [4,17]. In addition to verifying the presence of In2O3, the XRD results also reveal that the polycrystalline characteristics of the thin films are similar, regardless of the oxidation temperature. It must be noted, however, that the samples oxidized at 350°C and 450°C confirms incomplete oxidation owing to the presence of a peak assigned to indium metal. Even as the 550°C-oxidized sample did not show this peak, it cannot be ascertained that a complete oxidation of the indium metal was achieved.

 

Fig. 1 (a) SEM images of the In2O3/MgO films that were oxidized at different temperatures. The films are characterized by grain-like structures. (b) XRD data showing the polycrystalline nature of the films. The most intense peak is attributed to the MgO substrate while the rest are assigned to cubic-In2O3 structure. Results show that incomplete oxidation occurred due to the presence of a diffraction peak assigned to Indium metal.

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The THz-TDS data plots for sub-bandgap optical excitation (800 nm, 600 nJ/cm2 fluence) of the three samples are shown in Fig. 2 . To confirm that the THz transients did not originate from the MgO, a bare substrate was also tested yielding no THz emission. The 450°C film exhibited the most intense THz emission, followed by the In2O3/MgO film oxidized at 550°C. The 350°C film has a slightly weaker THz emission compared with the 550°C sample. The corresponding Fourier-transform amplitude spectra of the TDS waveforms (inset) revealed spectrally symmetric emission having a central frequency at 1 THz, with frequency components extending up to ~2 THz. The signal amplitude of the THz transients was approximately 10 times less than that of SI-GaAs and is two orders weaker than the THz emission from p-InAs. A recent survey of semiconductor surface THz emitters reported that p-InAs is currently the most intense semiconductor surface THz emitter [18] and thus, the observed THz emission from the In2O3 samples are very weak. However, the surveyed high-quality low-bandgap semiconductors were grown using well-established growth techniques, and were excited at energies well above the bandgap; hardly comparable with the conditions in this current study. With a signal-to-noise ratio dynamic range of approximately 1 order of magnitude in the amplitude spectra, the observed THz emission is sufficiently intense to warrant interest and further investigation. The THz data suggest a correlation between THz radiation and the presence of the cubic (222)-oriented c-In2O3 phase because XRD results showed that the 450°C-oxidized sample, having the highest THz emission, also exhibited the strongest intensity for this particular peak assignment. The presence of this phase appears to favor slightly more intense THz emission but this assertion needs further experimental confirmation and will not be pursued in detail in this work. On the other hand, it is important to have a better understanding of the underlying THz radiation mechanism albeit for sub-bandgap optical excitation.

 

Fig. 2 THz-TDS plots for the In2O3/MgO films oxidized at 350°C, 450°C, 550°C. The sample oxidized at 450°C exhibited the most intense THz emission. The inset shows the corresponding Fourier-transform spectra of the TDS data. The THz emission is centered at ~1 THz, and having frequency components of up to 2 THz. A signal-to-noise ratio dynamic range of more than 1 order of magnitude for the 450°C-oxidized sample illustrates implies intense THz emission.

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Initially, a two-photon absorption process was suspected. A two-photon photoconductive THz emission in ZnSe has been previously reported [19]. However, our further experimental verifications showed that photocarrier generation due to this nonlinear process is unlikely. The 2nd harmonic (400 nm at 40 mW) of the 800 nm wavelength emission of the Ti:Sapphire laser was used to excite the 450°C sample in order to investigate above-bandgap optical excitation. Its THz emission was then compared with the emission for the fundamental-line excitation at the same power. The results are shown in the inset of Fig. 3 , wherein the above-bandgap pump yielded lower THz emission. In general, the probability two-photon absorption is orders of magnitude lower than the single photon case and the comparable THz emission intensities in the inset do not support a dominant two-photon scenario. Moreover, even though the number of photons in the short-wavelength excitation case is only half of the fundamental line pumping, a two-photon process should still have exhibited less efficient photo-carrier generation (and THz emission). The difference in the THz-TDS waveforms in the two excitation conditions, however, suggests that the origin of photocarrier generation that leads to THz emission are different. The above-bandgap excitation case exhibited an almost single-cycle THz transient while the THz emission due to sub-bandgap absorption was characterized by several cycles. This is an indication of differences in the photocarrier dynamics between 400 nm and 800 nm excitation cases that could be an interesting topic for succeeding studies.

 

Fig. 3 Excitation fluence dependence of the THz emission from the 450°C-oxidized sample. The slope of the log-log plot indicates that the THz radiation mechanism is not a nonlinear optical process. The inset compares the THz emission from below-bandgap and above-bandgap excitation showing that the 800 nm wavelength pump is more efficient (the traces have been offset for ease of comparison); thereby ruling out a two-photon absorption process as the origin of the photo-carriers causing THz emission.

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Excitation fluence dependence measurements were then undertaken to further study the origin of the THz emission from the In2O3 films. The log-log plot of the fluence dependence in Fig. 3 did not exhibit a slope-2 dependence which would otherwise characterize a two-photon process [20]. The linear fluence dependence indicates that the origin of the THz emission could not be mainly attributed to two-photon absorption; although this possibility may not be completely excluded. Previous reports have demonstrated sub-bandgap excited THz emission in GaAs owing to the inverse Franz-Keldysh effect which is due to the third-order nonlinear susceptibility [21]. Similar results on the observation of THz emission via the second order nonlinear effect called optical rectification (OR) mechanism in sub-bandgap excited 6H-SiC [22] and in LiNbO3, LiTaO3, and dimethyl amino 4-N-methylstilbazolium tosylate (DAST) electro-optic crystals [23]. The OR THz emission mechanism does not necessitate photocarrier generation or above-bandgap excitation (as with the inverse Franz-Keldysh effect). However, these are nonlinear optical processes which are strictly dependent on the orientation of the crystal axis relative to the polarization of the optical excitation. In this regard, the OR mechanism is excluded as a possible THz radiation mechanism for the In2O3 samples in this study. The polycrystalline In2O3 film, comprising of different crystalline phases, is not favorable for OR-related THz emission [1]. More importantly, the azimuthal angle dependence of the THz emission was investigated and no distinct angular dependence was observed. This agrees well with the assertion that an OR-related nonlinear THz mechanism is improbable as the In2O3 films are polycrystalline.

The fluence dependence results also show that saturation of the THz emission occurs at about 400 nJ/cm2. This finding is currently being studied in more detail but the low saturation value could provide insights on the characteristics of the THz mechanism. Although room-temperature optical spectroscopy such as photoluminescence and transmittance in the NIR region did not yield any informative results, this sub-bandgap absorption near the excitation wavelength region is currently believed to be the origin of the photo-carriers responsible for THz generation. This weak absorption band could originate from still-unverified electronic states coming from defects and impurities similar to earlier reports, which are common in wide bandgap semiconductor such as In2O3 [24,25]. The actual origin of this absorption band could not be confirmed by deep level transient spectroscopy (DLTS) as well, due to the difficulty in fabricating electronic contacts. As the XRD data showed, incomplete oxidation, and therefore the presence of indium, prevented the preparation of devices suited for DLTS measurements. These photo-carriers from defect-related absorption are presumably driven by a strong, strain-induced electric field at the In2O3/MgO interface region. This strain field coming from the huge lattice mismatch (58.36%) between the In2O3 film and the MgO can facilitate carrier drift at the In2O3/MgO interface region, resulting in THz emission [15,26]. In Refs [10,11], a 5 nm-deep electron accumulation layer near its surface similar to InAs and InN, is implied as the main reason why In2O3 may be considered to be a contender for intense THz emission. However, the optical excitation conditions in this work suggest otherwise. The In2O3/MgO sample transmits most of the 800 nm-wavelength light and the sample’s estimated 1,100 nm film thickness (according to AFM measurements) is large compared with the 5 nm depth of the reported surface accumulation layer. It must be noted that the excitation laser is practically transmitted through the In2O3 film. Thus the THz emission due to carriers driven by a surface field in the accumulation layer should be negligible compared with the sub-bandgap absorption deep beneath the surface. As such, this situation agrees well with the conjecture that carrier drift at the strained interface region is a more probable origin of THz transients as opposed to a surface effect. Furthermore, Ref [10] provided experimental data for the effective mass and carrier mobility for In2O3, which are 0.35m0 and 32 cm2/(V.s), respectively. Aside from the fact that the sub-bandgap excitation results in carriers lacking excess energy required for photo-Dember emission, these nominal effective mass and carrier mobility values further suggest that a Dember-related mechanism is not favored. Thus, a field-driven photo-carrier drift should be the more plausible THz mechanism for the In2O3. The low saturation fluence exhibited by the samples could not be fully accounted for at this time. However, it is possible that long carrier lifetimes resulting in carrier accumulation and therefore, saturation could be a contributing factor. More so, defect-related states are prone to scattering [27] and should contribute to increased carrier lifetimes.

The presence of these defects has been shown not to detrimentally affect the THz emission properties of the In2O3/MgO sample in a significant manner. The micron-scale grain structures could scatter incident NIR light but the optical quality of the sample in the THz region has not been compromised. Shown in Fig. 4 is the comparison of the THz emission from the 450°C-oxidized sample in the transmission excitation geometry for the cases where the optical excitation was made incident on the film side and on the MgO substrate side. An important observation is that the peak intensities of the two signals are very much comparable. The intensity attenuation for the case of MgO substrate-side excitation is attributed to the attenuation of the excitation pump laser after passing through the MgO substrate, possibly due to reflection and optical scattering. As such, it can be deduced that: (a) the MgO substrate is sufficiently transparent to both the excitation beam and to THz radiation and (b) the In2O3 film is transparent to THz radiation.

 

Fig. 4 In the transmission-type excitation geometry, the THz emission intensity does not vary much whether the sample was excited from the MgO substrate side or from the In2O3 film side. Even as the sample’s over-all optical transmission is relatively low due to strong scattering, its THz optical qualities are not compromised. The TDS waveforms have been shifted for ease of comparison.

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4. Summary

This work experimentally demonstrated the generation of THz transients in polycrystalline In2O3 thin films on MgO substrates, prepared by thermal oxidation. Sufficiently intense THz emission can be observed even for excitation photon energy below the In2O3 bandgap of 2.9 eV. A comparison of the THz emission intensity between above- and sub-bandgap excitation initially suggested that a two-photon absorption process is not mainly responsible for the THz emission. This was confirmed by excitation fluence dependence measurements. The sub-bandgap absorption is currently attributed to weak absorption from defects and impurities although this has not been confirmed. Transmission excitation geometry THz measurements showed that the samples are sufficiently transparent in the THz region. Studies on the actual utilization of In2O3/MgO films in wide-bandgap PCA’s is beyond the scope of this work. However, results suggest that the necessity of short-wavelength excitation sources for such future devices may be circumvented owing to the observation of sub-bandgap excited THz emission from In2O3.

Acknowledgments

A. Somintac, R. V. Sarmago, and A. Salvador acknowledge support from DOST and UP OVCRD.

References and links

1. P. Gu and M. Tani, “Terahertz radiation from semiconductor surfaces,” in Terahertz Optoelectronics: Topics in Applied Physics, Vol. 97, K. Sakai, ed. (Springer-Verlag, 2005).

2. G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005). [CrossRef]  

3. S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005). [CrossRef]  

4. M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000). [CrossRef]  

5. R. L. Weiher and R. P. Ley, “Optical properties of indium oxide,” J. Appl. Phys. 37(1), 299–302 (1966). [CrossRef]  

6. R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009). [CrossRef]  

7. G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

8. V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010). [CrossRef]  

9. K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005). [CrossRef]  

10. P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009). [CrossRef]  

11. T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

12. P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007). [CrossRef]  

13. R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004). [CrossRef]  

14. N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998). [CrossRef]  

15. H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films 303(1–2), 216–221 (1997).

16. M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004). [CrossRef]  

17. M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

18. V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008). [CrossRef]  

19. J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett. 83(14), 2967–2969 (2003). [CrossRef]  

20. C. Soci and D. Moses, “Terahertz generation from poly(p-phenylene vinylene) photoconductive antenna,” Synth. Met. 139(3), 815–817 (2003). [CrossRef]  

21. B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett. 67(19), 2709–2712 (1991). [CrossRef]   [PubMed]  

22. J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009). [CrossRef]  

23. T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995). [CrossRef]  

24. M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008). [CrossRef]  

25. A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett. 4(6), 526–531 (2009). [CrossRef]   [PubMed]  

26. E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009). [CrossRef]  

27. K. Hess, Advanced Theory of Semiconductor Devices (Wiley Interscience, 2000).

References

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  1. P. Gu and M. Tani, “Terahertz radiation from semiconductor surfaces,” in Terahertz Optoelectronics: Topics in Applied Physics, Vol. 97, K. Sakai, ed. (Springer-Verlag, 2005).
  2. G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
    [Crossref]
  3. S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
    [Crossref]
  4. M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000).
    [Crossref]
  5. R. L. Weiher and R. P. Ley, “Optical properties of indium oxide,” J. Appl. Phys. 37(1), 299–302 (1966).
    [Crossref]
  6. R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009).
    [Crossref]
  7. G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).
  8. V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
    [Crossref]
  9. K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005).
    [Crossref]
  10. P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
    [Crossref]
  11. T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).
  12. P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007).
    [Crossref]
  13. R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004).
    [Crossref]
  14. N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998).
    [Crossref]
  15. H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films 303(1–2), 216–221 (1997).
  16. M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004).
    [Crossref]
  17. M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).
  18. V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008).
    [Crossref]
  19. J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett. 83(14), 2967–2969 (2003).
    [Crossref]
  20. C. Soci and D. Moses, “Terahertz generation from poly(p-phenylene vinylene) photoconductive antenna,” Synth. Met. 139(3), 815–817 (2003).
    [Crossref]
  21. B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett. 67(19), 2709–2712 (1991).
    [Crossref] [PubMed]
  22. J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
    [Crossref]
  23. T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995).
    [Crossref]
  24. M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
    [Crossref]
  25. A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett. 4(6), 526–531 (2009).
    [Crossref] [PubMed]
  26. E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
    [Crossref]
  27. K. Hess, Advanced Theory of Semiconductor Devices (Wiley Interscience, 2000).

2010 (1)

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

2009 (5)

R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009).
[Crossref]

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett. 4(6), 526–531 (2009).
[Crossref] [PubMed]

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

2008 (3)

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
[Crossref]

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008).
[Crossref]

2007 (1)

P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007).
[Crossref]

2006 (1)

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

2005 (3)

K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005).
[Crossref]

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

2004 (2)

R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004).
[Crossref]

M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004).
[Crossref]

2003 (2)

J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett. 83(14), 2967–2969 (2003).
[Crossref]

C. Soci and D. Moses, “Terahertz generation from poly(p-phenylene vinylene) photoconductive antenna,” Synth. Met. 139(3), 815–817 (2003).
[Crossref]

2000 (1)

M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000).
[Crossref]

1998 (1)

N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998).
[Crossref]

1997 (1)

H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films 303(1–2), 216–221 (1997).

1996 (1)

M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

1995 (1)

T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995).
[Crossref]

1991 (1)

B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett. 67(19), 2709–2712 (1991).
[Crossref] [PubMed]

1966 (1)

R. L. Weiher and R. P. Ley, “Optical properties of indium oxide,” J. Appl. Phys. 37(1), 299–302 (1966).
[Crossref]

Adomavicius, R.

V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008).
[Crossref]

Albe, K.

P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007).
[Crossref]

Almaral, A.

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

Alves, E.

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

Ambacher, O.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Ascázubi, R.

R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004).
[Crossref]

Auston, D. H.

B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett. 67(19), 2709–2712 (1991).
[Crossref] [PubMed]

Awitan, F. C. B.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Bechstedt, F.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Bell, G. R.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Bourlange, A.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

Cadatal-Raduban, M.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Carrig, T. J.

T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995).
[Crossref]

Chandrashekhar, M.

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

Choi, W. C.

M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

Cimalla, V.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Clement, T. S.

T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995).
[Crossref]

Conde, O.

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

Dawlaty, J.

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

Defensor, M.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Denniston, K.

R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004).
[Crossref]

Diwa, G.

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Donchev, I.

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

Egdell, R.

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007).
[Crossref]

Egdell, R. G.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Elezzabi, A. Y.

J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett. 83(14), 2967–2969 (2003).
[Crossref]

Erhart, P.

P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007).
[Crossref]

Estacio, E.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

Fortunato, E.

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

Fuchs, F.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Fuks, D.

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

Fukuda, T.

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Garcia, A.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

George, P. A.

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

Girtan, M.

M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000).
[Crossref]

Golovanov, V.

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

Gurlui, S.

M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000).
[Crossref]

Han, S.-H.

R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009).
[Crossref]

Hangyo, M.

M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004).
[Crossref]

Hesse, D.

H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films 303(1–2), 216–221 (1997).

Holzman, J. F.

J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett. 83(14), 2967–2969 (2003).
[Crossref]

Hu, B. B.

B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett. 67(19), 2709–2712 (1991).
[Crossref] [PubMed]

Ichikawa, Y.

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Ivanovskaya, M.

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

Izumida, S.

N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998).
[Crossref]

Jaculbia, R. B.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Kapse, H. N.

K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005).
[Crossref]

Kim, C. K.

M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

Kim, E. K.

M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

King, P.

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

King, P. D. C.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Kiv, A.

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

Klein, A.

P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007).
[Crossref]

Krotkus, A.

V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008).
[Crossref]

Kumar, M.

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
[Crossref]

Lakshmi, K. V.

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
[Crossref]

Lavareda, G.

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

Lee, M. S.

M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

Ley, R. P.

R. L. Weiher and R. P. Ley, “Optical properties of indium oxide,” J. Appl. Phys. 37(1), 299–302 (1966).
[Crossref]

Liu, C. C.

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

Liu, Z.

N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998).
[Crossref]

Lu, H.

R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004).
[Crossref]

Makhija, K. K.

K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005).
[Crossref]

Malevich, V. L.

V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008).
[Crossref]

Mane, R. S.

R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009).
[Crossref]

McConville, C.

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

McConville, C. F.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Mehta, B. R.

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
[Crossref]

Min, S.-K.

R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009).
[Crossref]

M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

Moses, D.

C. Soci and D. Moses, “Terahertz generation from poly(p-phenylene vinylene) photoconductive antenna,” Synth. Met. 139(3), 815–817 (2003).
[Crossref]

Murakami, H.

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Nagasaka, R.

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Nakajima, M.

M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004).
[Crossref]

Nakazato, T.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Nunes de Carvalho, C.

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

Ogino, H.

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Ohshima, E.

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Ohtake, H.

N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998).
[Crossref]

Ono, S.

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

Othonos, A.

A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett. 4(6), 526–531 (2009).
[Crossref] [PubMed]

Patel, R. M.

K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005).
[Crossref]

Payne, D.

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

Payne, D. J.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Pham, M. H.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Pobre, R.

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

Quema, A.

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Ramos, A. R.

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

Rana, F.

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

Ray, A.

K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005).
[Crossref]

Rodriguez, G.

T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995).
[Crossref]

Rusu, G. G.

M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000).
[Crossref]

Rusu, G. I.

M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000).
[Crossref]

Salvador, A.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Sarukura, N.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998).
[Crossref]

Schaff, W. J.

R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004).
[Crossref]

Senz, St.

H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films 303(1–2), 216–221 (1997).

Sharma, R.

R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009).
[Crossref]

Shimizu, T.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Shivaraman, S.

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

Sieber, H.

H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films 303(1–2), 216–221 (1997).

Singh, F.

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
[Crossref]

Singh, J. P.

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
[Crossref]

Singh, V. N.

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
[Crossref]

Smatko, V.

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

Soci, C.

C. Soci and D. Moses, “Terahertz generation from poly(p-phenylene vinylene) photoconductive antenna,” Synth. Met. 139(3), 815–817 (2003).
[Crossref]

Somintac, A.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Spencer, M. G.

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

Stewart, K. R.

T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995).
[Crossref]

Strait, J. H.

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

Takatori, S.

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Tani, M.

M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004).
[Crossref]

Taylor, A. J.

T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995).
[Crossref]

Trivedi, U. B.

K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005).
[Crossref]

Tsokkou, D.

A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett. 4(6), 526–531 (2009).
[Crossref] [PubMed]

Uchida, K.

M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004).
[Crossref]

Veal, T.

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

Veal, T. D.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Wang, Ch. Y.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Weiher, R. L.

R. L. Weiher and R. P. Ley, “Optical properties of indium oxide,” J. Appl. Phys. 37(1), 299–302 (1966).
[Crossref]

Wilke, I.

R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004).
[Crossref]

Yoshikawa, A.

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

Zervos, M.

A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett. 4(6), 526–531 (2009).
[Crossref] [PubMed]

Zhang, H.

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Zhang, X.-C.

B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett. 67(19), 2709–2712 (1991).
[Crossref] [PubMed]

Appl. Phys. Lett. (9)

G. Diwa, A. Quema, E. Estacio, R. Pobre, H. Murakami, S. Ono, and N. Sarukura, “Photonic-crystal-fiber pigtail device integrated with lens-duct optics for terahertz radiation coupling,” Appl. Phys. Lett. 87(15), 151114 (2005).
[Crossref]

S. Ono, H. Murakami, A. Quema, G. Diwa, N. Sarukura, R. Nagasaka, Y. Ichikawa, H. Ogino, E. Ohshima, A. Yoshikawa, and T. Fukuda, “Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses,” Appl. Phys. Lett. 87(26), 261112 (2005).
[Crossref]

R. Ascázubi, I. Wilke, K. Denniston, H. Lu, and W. J. Schaff, “Terahertz emission by InN,” Appl. Phys. Lett. 84(23), 4810–4812 (2004).
[Crossref]

M. Nakajima, K. Uchida, M. Tani, and M. Hangyo, “Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler,” Appl. Phys. Lett. 85(2), 191–193 (2004).
[Crossref]

J. F. Holzman and A. Y. Elezzabi, “Two-photon photoconductive terahertz generation in ZnSe,” Appl. Phys. Lett. 83(14), 2967–2969 (2003).
[Crossref]

J. H. Strait, P. A. George, J. Dawlaty, S. Shivaraman, M. Chandrashekhar, F. Rana, and M. G. Spencer, “Emission of terahertz radiation from SiC,” Appl. Phys. Lett. 95(5), 051912 (2009).
[Crossref]

T. J. Carrig, G. Rodriguez, T. S. Clement, A. J. Taylor, and K. R. Stewart, “Scaling of terahertz radiation via optical rectification in electro-optic crystals,” Appl. Phys. Lett. 66(2), 121–123 (1995).
[Crossref]

M. Kumar, V. N. Singh, F. Singh, K. V. Lakshmi, B. R. Mehta, and J. P. Singh, “On the origin of photoluminescence in indium oxide octahedron structures,” Appl. Phys. Lett. 92(17), 171907 (2008).
[Crossref]

E. Estacio, M. H. Pham, S. Takatori, M. Cadatal-Raduban, T. Nakazato, T. Shimizu, N. Sarukura, A. Somintac, M. Defensor, F. C. B. Awitan, R. B. Jaculbia, A. Salvador, and A. Garcia, “Strong enhancement of terahertz emission from GaAs in InAs/GaAs quantum dot structures,” Appl. Phys. Lett. 94(23), 232104 (2009).
[Crossref]

Appl. Surf. Sci. (1)

M. Girtan, G. I. Rusu, G. G. Rusu, and S. Gurlui, “Influence of oxidation conditions on the properties of indium oxide thin films,” Appl. Surf. Sci. 162–163, 492–498 (2000).
[Crossref]

Bull. Mater. Sci. (1)

K. K. Makhija, A. Ray, R. M. Patel, U. B. Trivedi, and H. N. Kapse, “Indium oxide thin film based ammonia gas and ethanol vapour sensor,” Bull. Mater. Sci. 28(1), 9–17 (2005).
[Crossref]

C. R. Phys. (1)

V. L. Malevich, R. Adomavičius, and A. Krotkus, “THz emission from semiconductor surfaces,” C. R. Phys. 9(2), 130–141 (2008).
[Crossref]

Compound Semicon. (1)

T. Veal, P. King, C. McConville, D. Payne, A. Bourlange, and R. Egdell, “Transparent oxides: MBE unmasks the real indium oxide,” Compound Semicon. 14(11), 27 (2008).

J. Alloy. Comp. (1)

R. Sharma, R. S. Mane, S.-K. Min, and S.-H. Han, “Optimization of growth on In2O3 nano-spheres thin films by electrodeposition for dye-sensitized solar cells,” J. Alloy. Comp. 479(1–2), 840–843 (2009).
[Crossref]

J. Appl. Phys. (2)

R. L. Weiher and R. P. Ley, “Optical properties of indium oxide,” J. Appl. Phys. 37(1), 299–302 (1966).
[Crossref]

N. Sarukura, H. Ohtake, S. Izumida, and Z. Liu, “High average-power THz radiation from femtosecond laser-irradiated InAs in a magnetic field and its elliptical polarization characteristics,” J. Appl. Phys. 84(1), 654–656 (1998).
[Crossref]

J. Mater. Sci. Mater. Electron. (1)

V. Smatko, V. Golovanov, C. C. Liu, A. Kiv, D. Fuks, I. Donchev, and M. Ivanovskaya, “Structural stability of In2O3 films as sensor materials,” J. Mater. Sci. Mater. Electron. 21(4), 360–363 (2010).
[Crossref]

J. Non-Cryst. Solids (1)

G. Lavareda, C. Nunes de Carvalho, E. Fortunato, A. R. Ramos, E. Alves, O. Conde, and A. Almaral, “Transparent thin film transistors based on indium oxide semiconductor,” J. Non-Cryst. Solids 352(23–25), 2311–2314 (2006).

Nanoscale Res. Lett. (1)

A. Othonos, M. Zervos, and D. Tsokkou, “Femtosecond carrier dynamics in In2O3 nanocrystals,” Nanoscale Res. Lett. 4(6), 526–531 (2009).
[Crossref] [PubMed]

Phys. Rev. B (2)

P. Erhart, A. Klein, R. Egdell, and K. Albe, “Band structure of indium oxide: Indirect versus direct band gap,” Phys. Rev. B 75(15), 153205 (2007).
[Crossref]

P. D. C. King, T. D. Veal, F. Fuchs, Ch. Y. Wang, D. J. Payne, A. Bourlange, H. Zhang, G. R. Bell, V. Cimalla, O. Ambacher, R. G. Egdell, F. Bechstedt, and C. F. McConville, “Band gap, electronic structure, and surface electron accumulation of cubic and rhombohedral In2O3,” Phys. Rev. B 79(20), 205211 (2009).
[Crossref]

Phys. Rev. Lett. (1)

B. B. Hu, X.-C. Zhang, and D. H. Auston, “Terahertz radiation induced by subband-gap femtosecond optical excitation of GaAs,” Phys. Rev. Lett. 67(19), 2709–2712 (1991).
[Crossref] [PubMed]

Synth. Met. (1)

C. Soci and D. Moses, “Terahertz generation from poly(p-phenylene vinylene) photoconductive antenna,” Synth. Met. 139(3), 815–817 (2003).
[Crossref]

Thin Solid Films (2)

H. Sieber, St. Senz, and D. Hesse, “Crystallographic orientation and morphology of epitaxial In2O3 thin films grown on MgO(001) single crystal substrates,” Thin Solid Films 303(1–2), 216–221 (1997).

M. S. Lee, W. C. Choi, E. K. Kim, C. K. Kim, and S.-K. Min, “Characterization of the oxidized indium thin films with thermal oxidation,” Thin Solid Films 279(1–2), 1–3 (1996).

Other (2)

P. Gu and M. Tani, “Terahertz radiation from semiconductor surfaces,” in Terahertz Optoelectronics: Topics in Applied Physics, Vol. 97, K. Sakai, ed. (Springer-Verlag, 2005).

K. Hess, Advanced Theory of Semiconductor Devices (Wiley Interscience, 2000).

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Figures (4)

Fig. 1
Fig. 1 (a) SEM images of the In2O3/MgO films that were oxidized at different temperatures. The films are characterized by grain-like structures. (b) XRD data showing the polycrystalline nature of the films. The most intense peak is attributed to the MgO substrate while the rest are assigned to cubic-In2O3 structure. Results show that incomplete oxidation occurred due to the presence of a diffraction peak assigned to Indium metal.
Fig. 2
Fig. 2 THz-TDS plots for the In2O3/MgO films oxidized at 350°C, 450°C, 550°C. The sample oxidized at 450°C exhibited the most intense THz emission. The inset shows the corresponding Fourier-transform spectra of the TDS data. The THz emission is centered at ~1 THz, and having frequency components of up to 2 THz. A signal-to-noise ratio dynamic range of more than 1 order of magnitude for the 450°C-oxidized sample illustrates implies intense THz emission.
Fig. 3
Fig. 3 Excitation fluence dependence of the THz emission from the 450°C-oxidized sample. The slope of the log-log plot indicates that the THz radiation mechanism is not a nonlinear optical process. The inset compares the THz emission from below-bandgap and above-bandgap excitation showing that the 800 nm wavelength pump is more efficient (the traces have been offset for ease of comparison); thereby ruling out a two-photon absorption process as the origin of the photo-carriers causing THz emission.
Fig. 4
Fig. 4 In the transmission-type excitation geometry, the THz emission intensity does not vary much whether the sample was excited from the MgO substrate side or from the In2O3 film side. Even as the sample’s over-all optical transmission is relatively low due to strong scattering, its THz optical qualities are not compromised. The TDS waveforms have been shifted for ease of comparison.

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