Center for Quantum Devices - Most Downloaded Journal Articles

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13.	Suppression of surface leakage in gate controlled type-II InAs/GaSb mid-infrared photodetectors G. Chen; B.-M. Nguyen; A.M. Hoang; E.K. Huang; S.R. Darvish; M. Razeghi Proc. SPIE 8268, Quantum Sensing and Nanophotonic Devices IX, 826811 (January 20, 2012)-- January 20, 2012 ...[Visit Journal] One of the biggest challenges of improving the electrical performance in Type II InAs/GaSb superlattice photodetector is suppressing the surface leakage. Surface leakage screens important bulk dark current mechanisms, and brings difficulty and uncertainty to the material optimization and bulk intrinsic parameters extraction such as carrier lifetime and mobility. Most of surface treatments were attempted beyond the mid-infrared (MWIR) regime because compared to the bulk performance, surface leakage in MWIR was generally considered to be a minor factor. In this work, we show that below 150K, surface leakage still strongly affects the electrical performance of the very high bulk performance p-π-M-n MWIR photon detectors. With gating technique, we can effectively eliminate the surface leakage in a controllable manner. At 110K, the dark current density of a 4.7 μm cut-off gated photon diode is more than 2 orders of magnitude lower than the current density in SiO₂ passivated ungated diode. With a quantum efficiency of 48%, the specific detecivity of gated diodes attains 2.5 x 10¹⁴ cm·Hz^1/2/W, which is 3.6 times higher than that of ungated diodes. [reprint (PDF)]
13.	Reliable GaN-based resonant tunneling diodes with reproducible room-temperature negative differential resistance C. Bayram, D.K. Sadana, Z. Vashaei and M. Razeghi SPIE Proceedings, Vol. 8268, p. 826827-- January 22, 2012 ...[Visit Journal] negative differential resistance (NDR). Compared to other negative resistance devices such as (Esaki) tunnel and transferred-electron devices, RTDs operate much faster and at higher temperatures. III-nitride materials, composed of AlGaInN alloys, have wide bandgap, high carrier mobility and thermal stability; making them ideal for high power high frequency RTDs. Moreover, larger conduction band discontinuity promise higher NDR than other materials (such as GaAs) and room-temperature operation. However, earlier efforts on GaN-based RTD structures have failed to achieve a reliable and reproducible NDR. Recently, we have demonstrated for the first time that minimizing dislocation density and eliminating the piezoelectric fields enable reliable and reproducible NDR in GaN-based RTDs even at room temperature. Observation of NDR under both forward and reverse bias as well as at room and low temperatures attribute the NDR behaviour to quantum tunneling. This demonstration marks an important milestone in exploring III-nitride quantum devices, and will pave the way towards fundamental quantum transport studies as well as for high frequency optoelectronic devices such as terahertz emitters based on oscillators and cascading structures. [reprint (PDF)]
13.	High performance GaAs/GaInP heterostructure bipolar transistors grown by low-pressure metal-organic chemical vapour deposition M Razeghi, F Omnes, M Defour, P Maurel, J Hu, E Wolk and D Pavlidis M Razeghi et al 1990 Semicond. Sci. Technol. 5 278-- December 11, 1989 ...[Visit Journal] The authors report the fabrication of high-quality GaAs/GaInP n-p-n heterojunction bipolar transistors grown by low-pressure metal-organic chemical vapour deposition on semi-insulating substrates. Various structures with homogeneous and graded bases have been fabricated. Doping profiles together with X-ray double diffraction patterns demonstrate the excellent control of growth parameters such as thicknesses, doping levels and interface quality. The static characteristics of the devices show current gains as high as 400, which is the highest value reported in that system [reprint (PDF)]
13.	*High quality AlN and GaN epilayers grown on (001) sapphire, (100) and (111) silicon substrates P. Kung, A. Saxler, X. Zhang, D. Walker, T.C. Wang, I. Ferguson, and M. Razeghi Applied Physics Letters 66 (22)-- May 29, 1995** ...[Visit Journal] The growth of high quality AlN and GaN thin films on basal plane sapphire, (100), and (111) silicon substrates is reported using low pressure metalorganic chemical vapor deposition. X-ray rocking curve linewidths of about 100 and 30 arcsec were obtained for AlN and GaN on sapphire, respectively. Room‐temperature optical transmission and photoluminescence (of GaN) measurements confirmed the high quality of the films. The luminescence at 300 and 77 K of the GaN films grown on basal plane sapphire, (100), and (111) silicon was compared. [reprint (PDF)]
13.	Progress in monolithic, broadband, widely tunable midinfrared quantum cascade lasers Manijeh Razeghi Wenjia Zhou Ryan McClintock Donghai Wu Steven Slivken Optical Engineering 57(1), 011018-- December 1, 2017 ...[Visit Journal] We present recent progress on the development of monolithic, broadband, widely tunable midinfrared quantum cascade lasers. First, we show a broadband midinfrared laser gain realized by a heterogeneous quantum cascade laser based on a strain balanced composite well design of Al_0.63In_0.37As∕Ga_0.35In_0.65As∕ Ga_0.47In_0.53As. Single mode emission between 5.9 and 10.9 μm under pulsed mode operation was realized from a distributed feedback laser array, which exhibited a flat current threshold across the spectral range. Using the broadband wafer, a monolithic tuning between 6.2 and 9.1 μm was demonstrated from a beam combined sampled grating distributed feedback laser array. The tunable laser was utilized for a fast sensing of methane under pulsed operation. Transmission spectra were obtained without any moving parts, which showed excellent agreement to a standard measurement made by a Fourier transform infrared spectrometer. [reprint (PDF)]
13.	Background limited performance of long wavelength infrared focal plane arrays fabricated from M-structure InAs/GaSb superlattices P.Y. Delaunay, B.M. Nguyen, D. Hoffman, E.K. Huang, P. Manurkar, S. Bogdanov and M. Razeghi SPIE Proceedings, San Jose, CA Volume 7222-0W-- January 26, 2009 ...[Visit Journal] Recent advances in the design and fabrication of Type-II InAs/GaSb superlattices allowed the realization of high performance long wavelength infrared focal plane arrays. The introduction of an Mstructure barrier between the n-type contact and the pi active region reduced the tunneling component of the dark current. The M-structure design improved the noise performance and the dynamic range of FPAs at low temperatures. At 81K, the NEDT of the focal plane array was 23 mK. The noise of the camera was dominated by the noise component due to the read out integrated circuit. At 8 µm, the median quantum efficiency of the detectors was 71%, mainly limited by the reflections on the backside of the array. [reprint (PDF)]
13.	MOCVD grown β-Ga₂O₃ metal-oxide-semiconductor field effect transistors on sapphire Ji-Hyeon Park , Ryan McClintock, Alexandre Jaud, Arash Dehzangi , Manijeh Razeghi Applied Physics Express 12, 095503-- August 28, 2019 ...[Visit Journal] We fabricated β-Ga₂O₃:Si metal-oxide field-effect transistors (MOSFETs) on c-plane sapphire substrates which typically showed maximum drain current of 100 mA·mm⁻¹. β-Ga₂O₃:Si thin films were realized on c-plane sapphire substrates through a combination of metalorganic chemical vapor deposition and post-annealing. The MOSFET device presented excellent on/off drain current ratio of ∼10¹¹ with very low gate leakage current, sharp pinch off behavior, and a breakdown voltage of 400 V at VG = −40 V. The growth and fabrication of β-Ga₂O₃:Si MOSFETs on c-plane sapphire is valuable to its demonstration of the great potential for future high-power electronic devices. [reprint (PDF)]
13.	Investigation of the Heteroepitaxial Interfaces in the GaInP/GaAs Superlattices by High Resolution X-Ray Diffraction and Dynamical Solutions Xiaoguang He and Manijeh Razeghi Journal of Applied Physics 73 (7)-- April 1, 1993 ...[Visit Journal] Two GaAs/GaInP superlattices grown on GaAs substrates by low‐pressure metalorganic chemical vapor deposition have been studied using high resolution x‐ray diffraction measurements and simulations by solving Tagaki–Taupin equations. The strained layers at both interfaces of the GaAs well are identified from the simulations of the measured diffraction patterns. The purging of indium at the interface of GaInP/GaAs accounts for the strained layer at the GaInP/GaAs interface while the pressure difference in the gas lines, which results in the different traveling time to the sample surface, is attributed to the indium‐poor strained layer at the GaAs/GaInP interface. It is shown that high‐resolution x‐ray diffraction measurements combined with a dynamical simulation, are sensitive tools to study the heteroepitaxial interfaces on an atomic layer scale. In addition, the influence of a miscut of the substrate on the measurement is discussed in the article. It is shown that even though the miscut is small, the diffraction geometry is already an asymmetric one. More than 10% error in the superlattice period for a 2° miscut substrate can result when the miscut substrate is considered a symmetric geometry. [reprint (PDF)]
13.	Ridge-Width Dependence on High-Temperature Continuous-Wave Quantum-Cascade Laser Operation S. Slivken, J.S. Yu, A. Evans, L. Doris, J. David, and M. Razeghi IEEE Photonics Technology Letters, 16 (3)-- March 1, 2004 ...[Visit Journal] We report continuous-wave (CW) operation of quantum-cascade lasers (λ=6 μm) up to a temperature of 313 K (40°C). The maximum CW optical output powers range from 212 mW at 288 K to 22 mW at 313 K and are achieved with threshold current densities of 2.21 and 3.11 kA/cm2, respectively, for a high-reflectivity-coated 12-μm-wide and 2-mm-long laser. At room temperature (298 K), the power output is 145 mW at 0.87 A, corresponding to a power conversion efficiency of 1.68%. The maximum CW operating temperature of double-channel ridge waveguide lasers mounted epilayer-up on copper heatsinks is analyzed in terms of the ridge width, which is varied between 12 and 40 μm. A clear trend of improved performance is observed as the ridge narrows. [reprint (PDF)]
13.	Deep Fe and intrinsic defect levels in Ga0.47In0.53As/InP K.‐H. Goetz; D. Bimberg; K.‐A. Brauchle; H. Jürgensen; J. Selders; M. Razeghi; E. Kuphal K.‐H. Goetz, D. Bimberg, K.‐A. Brauchle, H. Jürgensen, J. Selders, M. Razeghi, E. Kuphal; Deep Fe and intrinsic defect levels in Ga0.47In0.53As/InP. Appl. Phys. Lett. 1 February 1985; 46-- February 1, 1985 ...[Visit Journal] Two deep traps in Ga0.47In0.53As/InP:Fe at a depth of 110 meV and 150 meV, respectively, are observed for the first time using low‐temperature photoluminescence and deep level transient spectroscopy. The dependence of luminescence intensity on the growth process itself (liquid phase epitaxy, vapor phase epitaxy, and metalorganic chemical vapor deposition) and its parameters (growth temperature, layer thickness) and the substrate doping is reported and leads to the unambigous identification of the 150‐meV acceptorlike trap as being caused by Fe impurities. Fe diffuses from the substrate to the epitaxial layer during the growth process. This outdiffusion is less pronounced for layers grown at lower temperature. The level at 110 meV which is also observed in layers grown on InP:S substrate is tentatively assigned to an intrinsic defect of Ga0.47In0.53As. [reprint (PDF)]
13.	Tunability of intersubband absorption from 4.5 to 5.3 µm in a GaN/Al_0.2Ga_0.8N superlattices grown by metalorganic chemical vapor deposition N. Péré-Laperne, C. Bayram, L. Nguyen-Thê, R. McClintock, and M. Razeghi Applied Physics Letters, Vol. 95, No. 13, p. 131109-- September 28, 2009 ...[Visit Journal] Intersubband (ISB) absorption at wavelengths as long as 5.3 µm is realized in GaN/Al_0.2Ga_0.8N superlattices grown by metalorganic chemical vapor deposition. By employing low aluminum content Al_0.2Ga_0.8N barriers and varying the well width from 2.6 to 5.1 nm, ISB absorption has been tuned from 4.5 to 5.3 µm. Theoretical ISB absorption and interband emission models are developed and compared to the experimental results. The effects of band offsets and the piezoelectric fields on these superlattices are investigated. [reprint (PDF)]
13.	Electrically pumped photonic crystal distributed feedback quantum cascade lasers Y. Bai, S.R. Darvish, S. Slivken, P. Sung, J. Nguyen, A. Evans, W. Zhang, and M. Razeghi Applied Physics Letters, Vol. 91, No. 14, p. 141123-1-- October 1, 2007 ...[Visit Journal] We demonstrate electrically pumped, room temperature, single mode operation of photonic crystal distributed feedback (PCDFB) quantum cascade lasers emitting at ~4.75 µm. Ridge waveguides of 100 µm width were fabricated with both PCDFB and Fabry-Pérot feedback mechanisms. The Fabry-Pérot device has a broad emitting spectrum and a double lobed far-field character. The PCDFB device, as expected, has primarily a single spectral mode and a diffraction limited far field characteristic with a full angular width at half maximum of 2.4°. This accomplishment represents the first step in power scaling of single mode, midinfrared laser diodes operating at room temperature. [reprint (PDF)]
13.	Toward realizing high power semiconductor terahertz laser sources at room temperature Manijeh Razeghi Proc. SPIE 8023, Terahertz Physics, Devices, and Systems V: Advance Applications in Industry and Defense, 802302 (May 25, 2011)-- May 25, 2011 ...[Visit Journal] The terahertz (THz) spectral range offers promising applications in science, industry, and military. THz penetration through nonconductors (fabrics, wood, plastic) enables a more efficient way of performing security checks (for example at airports), as illegal drugs and explosives could be detected. Being a non-ionizing radiation, THz radiation is environment-friendly enabling a safer analysis environment than conventional X-ray based techniques. However, the lack of a compact room temperature THz laser source greatly hinders mass deployment of THz systems in security check points and medical centers. In the past decade, tremendous development has been made in GaAs/AlGaAs based THz Quantum Cascade Laser (QCLs), with maximum operating temperatures close to 200 K (without magnetic field). However, higher temperature operation is severely limited by a small LO-phonon energy (∼ 36 meV) in this material system. With a much larger LO-phonon energy of ∼ 90 meV, III-Nitrides are promising candidates for room temperature THz lasers. However, realizing high quality material for GaN-based intersubband devices presents a significant challenge. Advances with this approach will be presented. Alternatively, recent demonstration of InP based mid-infrared QCLs with extremely high peak power of 120 W at room temperature opens up the possibility of producing high power THz emission with difference frequency generation through two mid-infrared wavelengths. [reprint (PDF)]
13.	Background limited performance of long wavelength infrared focal plane arrays fabricated from type-II InAs/GaSb M-structure superlattice P.Y. Delaunay, B.M. Nguyen and M. Razeghi SPIE Porceedings, Vol. 7298, Orlando, FL 2009, p. 72981Q-- April 13, 2009 ...[Visit Journal] Recent advances in growth techniques, structure design and processing have lifted the performance of Type-II InAs/GaSb superlattice photodetectors. The introduction of a M-structure design improved both the dark current and R0A of Type-II photodiodes. This new structure combined with a thick absorbing region demonstrated background limited performance at 77K for a 300K background and a 2-π field of view. A focal plane array with a 9.6 μm 50% cutoff wavelength was fabricated with this design and characterized at 80K. The dark current of individual pixels was measured around 1.3 nA, 7 times lower than previous superlattice FPAs. This led to a higher dynamic range and longer integration times. The quantum efficiency of detectors without anti-reflective coating was 72%. The noise equivalent temperature difference reached 23 mK. The deposition of an anti-reflective coating improved the NEDT to 20 mK and the quantum efficiency to 89%. [reprint (PDF)]
13.	Stability of far fields in double heterostructure and multiple quantum well InAsSb/InPAsSb/InAs midinfrared lasers H. Yi, A. Rybaltowski, J. Diaz, D. Wu, B. Lane, Y. Xiao, and M. Razeghi Applied Physics Letters 70 (24)-- June 16, 1997 ...[Visit Journal] Far fields in perpendicular direction to the junction are investigated in double heterostructure (DH) and multiple quantum well (MQW) midwave-infrared InAsSb/InPAsSb/InAs lasers (λ = 3.2–3.6 μm). Strong broadening of the far fields in the DH lasers was observed with increases in temperature and/or current. On the contrary, MQW lasers with otherwise identical structure exhibit very stable far fields as narrow as 23° for all the operating conditions investigated. Our experiment and theoretical modeling suggest that these different behaviors of far fields in DH and MQW lasers are attributed to the refractive index fluctuation in the InAsSb laser active region. [reprint (PDF)]
13.	Widely Tunable, Single-Mode, High-Power Quantum Cascade Lasers M. Razeghi, B. Gokden, S. Tsao, A. Haddadi, N. Bandyopadhyay, and S. Slivken SPIE Proceedings, Intergreated Photonics: Materials, Devices and Applications, SPIE Microtechnologies Symposium, Prague, Czech Republic, April 18-20, 2011, Vol. 8069, p. 806905-1-- May 31, 2011 ...[Visit Journal] We demonstrate widely tunable high power distributed feedback quantum cascade laser array chips that span 190 nm and 200 nm from 4.4 um to 4.59 um and 4.5 um to 4.7 um respectively. The lasers emit single mode with a very narrow linewidth and side mode suppression ratio of 25 dB. Under pulsed operation power outputs up to 1.85 W was obtained from arrays with 3 mm cavity length and up to 0.95 W from arrays with 2 mm cavity length at room temperature. Continuous wave operation was also observed from both chips with 2 mm and 3 mm long cavity arrays up to 150 mW. The cleaved size of the array chip with 3 mm long cavities was around 4 mm x 5 mm and does not require sensitive external optical components to achieve wide tunability. With their small size and high portability, monolithically integrated DFB QCL Arrays are prominent candidates of widely tunable, compact, efficient and high power sources of mid-infrared radiation for gas sensing. [reprint (PDF)]
13.	Gallium nitride on silicon for consumer & scalable photonics C. Bayram, K.T. Shiu, Y. Zhu, C.W. Cheng, D.K. Sadana, Z. Vashaei, E. Cicek, R. McClintock and M. Razeghi SPIE Proceedings, Vol. 8631, p. 863112-1, Photonics West, San Francisco, CA-- February 4, 2013 ...[Visit Journal] Gallium Nitride (GaN) is a unique material system that has been heavily exploited for photonic devices thanks to ultraviolet-to-terahertz spectral tunability. However, without a cost effective approach, GaN technology is limited to laboratory demonstrations and niche applications. In this investigation, integration of GaN on Silicon (100) substrates is attempted to enable widespread application of GaN based optoelectronics. Controlled local epitaxy of wurtzite phase GaN on on-axis Si(100) substrates is demonstrated via metal organic chemical vapor deposition (MOCVD). CMOS-compatible fabrication scheme is used to realize [SiO2-Si{111}-Si{100}] groove structures on conventional 200-mm Si(100) substrates. MOCVD growth (surface treatment, nucleation, initiation) conditions are studied to achieve controlled GaN epitaxy on such grooved Si(100) substrates. Scanning electron microscopy and transmission electron microscopy techniques are used to determine uniformity and defectivity of the GaN. Our results show that aforementioned groove structures along with optimized MOCVD growth conditions can be used to achieve controlled local epitaxy of wurtzite phase GaN on on-axis Si(100) substrates. [reprint (PDF)]
13.	High-speed, low-noise metal-semiconductor-metal ultraviolet photodetectors based on GaN D. Walker, E. Monroy, P. Kung, J. Wu, M. Hamilton, F.J. Sanchez, J. Diaz, and M. Razeghi Applied Physics Letters 74 (5)-- February 1, 1999 ...[Visit Journal] We present the fabrication and characterization of nonintentionally doped GaN and GaN:Mg Schottky metal–semiconductor–metal (MSM) photodetectors, grown on sapphire by metalorganic chemical vapor deposition. Low-leakage, Schottky contacts were made with Pt/Au. The devices are visible blind, with an ultraviolet/green contrast of about five orders of magnitude. The response times of the MSM devices were <10 ns and about 200 ns for GaN and GaN:Mg, respectively. The noise power spectral density remains below the background level of the system (10−24 A²/Hz) up to 5 V, for the undoped GaN MSM detector. [reprint (PDF)]
13.	Improved performance of quantum cascade lasers via manufacturable quality epitaxial side down mounting process utilizing aluminum nitride heatsinks A. Tsekoun, R. Go, M. Pushkarsky, M. Razeghi, C.K.N. Patel SPIE Conference, San Jose, CA, Vol. 6127, pp. 612702-- January 23, 2006 ...[Visit Journal] We report substantially improved performance of high power quantum cascade lasers by utilizing epi-side down mounting that provides superior heat dissipation properties. We have obtained CW power output of 450 mW at 20°C from mid-IR QCLs. The improved thermal management achieved with epi-side down mounting has also permitted us to carry out initial lifetime tests on the mid-IR QCLs. No degradation of power output is seen even after over 300 hours of CW operation at 25°C with power output in excess of 300 mW. We believe these improvements should permit incorporation of mid-IR QCLs in reliable instrumentation. [reprint (PDF)]
13.	Sharp/Tuneable UVC Selectivity and Extreme Solar Blindness in Nominally Undoped Ga2O3 MSM Photodetectors Grown by Pulsed Laser Deposition D. J. Rogers, A. Courtois, F. H. Teherani, V. E. Sandana, P. Bove, X. Arrateig, L. Damé, P. Maso, M. Meftah, W. El Huni, Y. Sama, H. Bouhnane, S. Gautier, A. Ougazzaden & M. Razeghi Proc. SPIE 11687 (2021) 116872D-1 ...[Visit Journal] Ga2O3layers were grown on c-sapphire substrates by pulsed laser deposition. Optical transmission spectra were coherent with a bandgap engineering from 4.9 to 6.2 eV controlled via the growth conditions. X-ray diffraction revealed that the films were mainly β-Ga2O3(monoclinic) with strong (-201) orientation. Metal-Semiconductor-Metal photodetectors based on gold/nickel Inter- Digitated-Transducer structures were fabricated by single-step negative photolithography. 240 nm peak response sensors gave over 2 orders-of-magnitude of separation between dark and light signal with state-of-the-art solar and visible rejection ratios ((I240 : I290) of > 3 x 105 and (I240 : I400) of > 2 x 106) and dark signals of <50 pA (at a bias of -5V). Spectral responsivities showed an exceptionally narrow linewidth (16.5 nm) and peak values exhibited a slightly superlinear increase with applied bias up to a value of 6.5 A/W (i.e. a quantum efficiency of > 3000%) at 20V bias. [reprint (PDF)]
13.	High‐purity GaAs layers grown by low‐pressure metalorganic chemical vapor deposition M. Razeghi; F. Omnes; J. Nagle; M. Defour; O. Acher; P. Bove Appl. Phys. Lett. 55, 1677–1679 (1989)-- October 16, 1989 ...[Visit Journal] We report electrical and optical properties of very high purity GaAs epilayers grown by low‐pressure metalorganic chemical vapor deposition using AsH3 and triethylgallium as As and Ga sources. An electron mobility of 335 000 cm2/V s at 38 K has been measured for a 12‐μ‐thick layer. [reprint (PDF)]
13.	Room Temperature Operation of InTlSb Infrared Photodetectors on GaAs J.D. Kim, E. Michel, S. Park, J. Xu, S. Javadpour and M. Razeghi Applied Physics Letters 69 (3)-- August 15, 1996 ...[Visit Journal] Long-wavelength InTlSb photodetectors operating at room temperature are reported. The photo- detectors were grown on (100) semi-insulating GaAs substrates by low-pressure metalorganic chemical vapor deposition. Photoresponse of InTlSb photodetectors is observed up to 11 µm at room temperature. The maximum responsivity of an In_0.96Tl_0.04Sb photodetector is about 6.64 V/W at 77 K, corresponding to a detectivity of about 7.64 × 10⁸ cm·Hz^½/W. The carrier lifetime in InTlSb photodetectors derived from the stationary photoconductivity is 10–50 ns at 77 K. [reprint (PDF)]
13.	ZnO nanorod electrodes for hydrogen evolution and storage Harinipriya, S.; Usmani, B.; Rogers, D. J.; Sandana, V. E.; Teherani, F. Hosseini; Lusson, A.; Bove, P.; Drouhin, H.-J.; Razeghi, M. Proc. SPIE 8263, Oxide-based Materials and Devices III, 82631Y (February 9, 2012)-- February 9, 2012 ...[Visit Journal] Due to the attractive combination of a relatively high specific heat of combustion with a large specific energy capacity, molecular hydrogen (H2) is being investigated for use as an alternative to fossil fuels. Energy-efficient H₂ production and safe storage remain key technical obstacles to implementation of an H₂ based economy, however. ZnO has been investigated for use as an alternative photocatalytic electrode to TiO₂ for solarpowered photo-electro-chemical (PEC) electrolysis, in which H₂ is generated by direct water splitting in a cell with a metal cathode and a semiconducting anode. In this investigation, ZnO NR grown on Si (100) substrates by pulsed laser deposition were investigated for use as electrodes in the Hydrogen Evolution Reaction (HER). The electrochemical potential and Fermi energy of the ZnO NR were estimated from the electrochemical current density in acid and alkaline solutions via phenomenological thermodynamic analysis. As well as acting as an effective electrocalytic cathode, the ZnO NR appear to operate as a hydrogen reservoir. These results indicate that the ZnO NR have excellent potential for the storage of evolved H₂. [reprint (PDF)]
13.	Quantum oscillations at a Ga0.47In0.53AsInP heterojunction interface R.J Nicholas a, M.A Brummell a , J.C Portal b, M Razeghi c, M.A Poisson R.J Nicholas, M.A Brummell, J.C Portal, M Razeghi, M.A Poisson, Quantum oscillations at a Ga0.47In0.53AsInP heterojunction interface, Solid State Communications, Volume 43, Issue 11, 1982, Pages 825-828,-- September 1, 1982 ...[Visit Journal] We report the observation of a two dimensional gas of high mobility electrons at the interface of a Ga0.47In0.53AsInP heterojunction grown by MOCVD. The two dimensional electron concentrations and effective mass are determined by Shubnikov-de Haas studies, and compared with theoretical predictions. Evidence of an enhancement of the g-factor is observed. We also report observations of very pronounced quantum Hall steps as seen in GaAs-GaAlAs heterojunctions. [reprint (PDF)]
13.	Recent advances in III-Nitride materials, characterization and device applications M. Razeghi, X. Zhang, P. Kung, A. Saxler, D. Walker, K.Y. Lim, and K.S. Kim SPIE Conference: Solid State Crystals in Optoelectronics and Semiconductor Technology; Proceedings 3179-- October 7, 1996 ...[Visit Journal] High-quality AlN, GaN, AlGaN have been grown on sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The x-ray rocking curve of AlN and GaN were 100 arcsecs and 30 arcsecs respectively with Pendelloesung oscillations, which are the best reported to date. GaN with high crystallinity simultaneously exhibited high optical and electrical quality. Photoluminescence linewidth of GaN at 77K was as low as 17 meV, which is the best reported to date. Si-doped GaN had a mobility higher than 300 cm²/V·s. GaN has been also successfully grown on LiGaO₂ substrate with LP-MOCVD for the first time. AlGaN for the entire composition range has been grown. These layers exhibited the lowest x-ray FWHM reported to date. The excellent optical quality of these layers have been characterized by room temperature UV transmission and photoluminescence. N-type doping of AlGaN with Si has ben achieved up to 60 percent Al with mobility as high as 78 cm²/V·s. Al_xGa_1-xN/Al_yGa_1-yN superlattice with atomically sharp interface have been demonstrated. Optically-pumped stimulated emission in GaN:Ge and GaN:Si has been observed with threshold optical power density as low as 0.4 MW/cm². AlGaN photoconductors with cut-off wavelengths from 200 nm to 365 nm have been achieved for the first time. GaN p-n junction photovoltaic detector with very selective photoresponse have been demonstrated and theoretically modeled. Ti/AlN/Si metal-insulator- semiconductor capacitor with high capacitance-voltage performances at both low and high frequencies and low interface trap level density have been demonstrated for the first time in this material system. [reprint (PDF)]

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