Center for Quantum Devices - Most Downloaded Journal Articles

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17.	Investigations on the substrate dependence of the properties in nominally-undoped β-Ga2O3 thin films grown by PLD F. H. Teherani ; D. J. Rogers ; V. E. Sandana ; P. Bove ; C. Ton-That ; L. L. C. Lem ; E. Chikoidze ; M. Neumann-Spallart ; Y. Dumont ; T. Huynh ; M. R. Phillips ; P. Chapon ; R. McClintock ; M. Razeghi Proc. SPIE 10105, Oxide-based Materials and Devices VIII, 101051R-OLD-- March 23, 2017 ...[Visit Journal] Nominally-undoped Ga₂O₃ layers were deposited on a-, c- and r-plane sapphire substrates using pulsed laser deposition. Conventional x-ray diffraction analysis for films grown on a- and c-plane sapphire showed the layers to be in the β-Ga₂O₃ phase with preferential orientation of the (-201) axis along the growth direction. Pole figures revealed the film grown on r-plane sapphire to also be in the β-Ga₂O₃ phase but with epitaxial offsets of 29.5°, 38.5° and 64° from the growth direction for the (-201) axis. Optical transmission spectroscopy indicated that the bandgap was ~5.2eV, for all the layers and that the transparency was > 80% in the visible wavelength range. Four point collinear resistivity and Van der Pauw based Hall measurements revealed the β-Ga₂O₃ layer on r-plane sapphire to be 4 orders of magnitude more conducting than layers grown on a- and c-plane sapphire under similar conditions. The absolute values of conductivity, carrier mobility and carrier concentration for the β-Ga₂O₃ layer on r-sapphire (at 20Ω-1.cm^-1, 6 cm²/Vs and 1.7 x 10¹⁹ cm^-3, respectively) all exceeded values found in the literature for nominally-undoped β-Ga₂O₃ thin films by at least an order of magnitude. Gas discharge optical emission spectroscopy compositional depth profiling for common shallow donor impurities (Cl, F, Si and Sn) did not indicate any discernable increase in their concentrations compared to background levels in the sapphire substrate. It is proposed that the fundamentally anisotropic conductivity in β-Ga₂O₃ combined with the epitaxial offset of the (-201) axis observed for the layer grown on r-plane sapphire may explain the much larger carrier concentration, electrical conductivity and mobility compared with layers having the (-201) axis aligned along the growth direction. [reprint (PDF)]
17.	AlGaN ultraviolet detectors M. Razeghi and A. Rogalski, SPIE Conference, San Jose, CA, -- February 12, 1997 ...[Visit Journal] Hitherto, the semiconductor ultraviolet (UV) detectors have been mainly fabricated using Si. Industries such as the aerospace, automotive, petroleum, and others have continuously provided the impetus pushing the development of fringe technologies which are tolerant of increasingly high temperatures and hostile environments. As a result, the main efforts are currently directed to anew generation of UV detectors fabricated from wide-band-gap semiconductors between them the most promising are diamond and AlGaN. The latest progress in development of AlGaN UV detectors is described in detail. [reprint (PDF)]
17.	Thermal characteristics and analysis of quantum cascade lasers for biochemical sensing applications J.S. Yu, H.K. Lee, S. Slivken, and M. Razeghi SPIE Proceedings, Biosensing II, San Diego, CA (August 2-6, 2009), Vol. 7397, p. 739705-1-- August 2, 2009 ...[Visit Journal] We studied the thermal characteristics and analysis of InGaAs/InAlAs quantum cascade lasers (QCLs) in terms of internal temperature distribution, heat flux, and thermal conductance from the heat transfer simulation. The heat source densities were obtained from threshold power densities measured experimentally for QCLs under room-temperature continuous-wave operation. The use of a thick electroplated Au around the laser ridges helps increase the heat removal from devices. The two-dimensional anisotropic heat dissipation model was used to analyze the thermal behaviors inside the device. The simulation results were also compared with those estimated from experimental data. [reprint (PDF)]
17.	Short Wavelength Solar-Blind Detectors: Status, Prospects, and Markets M. Razeghi IEEE Proceedings, Wide Bandgap Semiconductor Devices: The Third Generation Semiconductor Comes of Age 90 (6)-- June 1, 2002 ...[Visit Journal] Recent advances in the research work on III-nitride semiconductors and Al_xGa_1-xN materials in particular has renewed the interest and led to significant progress in the development of ultraviolet (UV) photodetectors able to detect light in the mid- and near-UV spectral region (λ∼200-400 nm). There have been a growing number of applications which require the use of such sensors and, in many of these, it is important to be able to sense UV light without detecting infrared or visible light, especially from the Sun, in order to minimize the chances of false detection or high background. The research work on short-wavelength UV detectors has, therefore, been recently focused on realizing short-wavelength "solar-blind" detectors which, by definition, are insensitive to photons with wavelengths longer than ∼285 nm. In this paper the development of Al_xGa_1-xN-based solar-blind UV detectors will be reviewed. The technological issues pertaining to material synthesis and device fabrication will be discussed. The current state-of-the-art and future prospects for these detectors will be reviewed and discussed. [reprint (PDF)]
17.	Comparison of Gain and Threshold Current Density for InGaAsP/GaAs λ = 808 nm) Lasers with Different Quantum-Well Thickness H.J. Yi, J. Diaz, I. Eliashevich, G. Lukas, S. Kim, D. Wu, M. Erdtmann, C. Jelen, S. Slivken, L.J. Wang, and M. Razeghi Journal of Applied Physics 79 (11)-- July 1, 1996 ...[Visit Journal] We investigated the quantum‐size effects of quantum well (QW) on gain and threshold current density for InGaAsP/GaAs (λ=808 nm) laser diodes. In this work, a comparison is made of lasers with different QW thickness while keeping the optical confinement factors constant. We found that the threshold current density and differential efficiency were not affected by narrowing the QW thickness. The theoretical model taking into account the mixing of the valence bands and momentum relaxation for InGaAsP/GaAs lasers with spontaneous emission (optically pumped) measurement shows that the absence of difference between these structures can be attributed to the high relaxation rate. [reprint (PDF)]
17.	Quantum Dot Infrared Photodetectors: Comparison Experiment and Theory H. Lim, W. Zhang, S. Tsao, T. Sills, J. Szafraniec, K. Mi, B. Movaghar, and M. Razeghi Physical Review B, 72-- August 17, 2005 ...[Visit Journal] We present data and calculations and examine the factors that determine the detectivities in self-assembled InAs and InGaAs based quantum dot infrared photodetectors (QDIPs). We investigate a class of devices that combine good wavelength selectivity with “high detectivity.” We study the factors that limit the temperature performance of quantum dot detectors. For this we develop a formalism to evaluate the optical absorption and the electron transport properties. We examine the performance limiting factors and compare theory with experimental data. We find that the notion of a phonon bottleneck does not apply to large-diameter lenslike quantum dots, which have many closely spaced energy levels. The observed strong decrease of responsivity with temperature is ultimately due to a rapid thermal cascade back into the ground states. High temperature performance is improved by engineering the excited state to be near the continuum. The good low temperature (77 K) performance in strongly bound QDIPs is shown to be due to the high gain and the low noise achievable in these micron size devices. [reprint (PDF)]
17.	Temperature dependence of threshold current density J_th and differential efficiency of High Power InGaAsP/GaAs ( λ = 0.8 μm) lasers H. Yi, J. Diaz, I. Eliashevich, M. Stanton, M. Erdtmann, X. He, L. Wang, and M. Razeghi Applied Physics Letters 66 (3)-- January 16, 1995 ...[Visit Journal] An experimental and theoretical study on temperature dependence of the threshold current density J_th and differential efficiency ηd for the InGaAsP/GaAs laser diodes emitting at λ=0.8 μm was performed. Threshold current density J_th increases and differential efficiency η_d decreases as temperature is increased mainly because of thermal broadening of the gain spectrum. However, the measured temperature dependence of J_th and η_d could not be explained when only this effect was considered. In this letter, the temperature dependence of momentum relaxation rate ℏ/τ of carriers was investigated by performing the photoluminescence study. At high temperature, increase of the momentum relaxation rate ℏ/τ leads to reduction of the gain and mobility and increase of the optical loss, causing higher J_th and lower η_d as experimentally observed. The resulting theoretical model provides a good explanation for the mechanism of the increase of J_th and decrease of η_d. [reprint (PDF)]
17.	Persistent photoconductivity and the quantized Hall effect in In0.53Ga0.47As/InP heterostructures H. P. Wei; D. C. Tsui; M. Razeghi H. P. Wei, D. C. Tsui, M. Razeghi; Persistent photoconductivity and the quantized Hall effect in In0.53Ga0.47As/InP heterostructures. Appl. Phys. Lett. 15 September 1984; 45 (6): 666–668.-- September 15, 1984 ...[Visit Journal] A persistent photoconductivity is observed in the transport of the high mobility two‐dimensional electron gas in In0.53Ga0.47 As/InP heterostructures. Low field Hall measurements from 300 to 4.2 K and the quantized Hall effect in the high field limit are studied with radiation from visible and infrared light‐emitting diodes. Our results demonstrate conclusively that the effect is due to photogeneration of electron‐hole pairs in the heterostructure and trapping of holes in the In0.53Ga0.47 As. [reprint (PDF)]
16.	Room-temperature, high-power and continuous-wave operation of distributed-feedback quantum-cascade lasers at λ ~ 9.6 µm S.R. Darvish, S. Slivken, A. Evans, J.S. Yu, and M. Razeghi Applied Physics Letters, 88 (20)-- May 15, 2006 ...[Visit Journal] High-power continuous-wave (cw) operation of distributed-feedback quantum-cascade lasers is reported. Continuous-wave output powers of 100 mW at 25 °C and 20 mW at 50 °C are obtained. The device exhibits a cw threshold current density of 1.34 kA/cm², a maximum cw wall-plug efficiency of 1% at 25 °C, and a characteristic temperature of ~190 K in pulsed mode. Single-mode emission near 9.6 μm with a side-mode suppression ratio of ≥ 30 dB and a tuning range of 2.89 cm^–1 from 15 to 50 °C is obtained. [reprint (PDF)]
16.	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)]
16.	Emerging materials for photonics Miriam S. Vitiello, and Manijeh Razeghi APL Materials 5, 03510-- March 31, 2017 ...[Visit Journal] Photonics plays a major role in all aspects of human life. It revolutionized science by addressing fundamental scientiﬁc questions and by enabling key functions in many interdisciplinary ﬁelds spanning from quantum technologies to information andcommunicationscience,andfrombiomedicalresearchtoindustrialprocessmonitoring and life entertainment. [reprint (PDF)]
16.	Investigation of the factors influencing nanostructure array growth by PLD towards reproducible wafer-scale growth Vinod E. Sandana; David. J. Rogers; Ferechteh Hosseini Teherani; Philippe Bove; Manijeh Razeghi physica status solidi (a) Applications and Materials Science. Volume 211, Issue 2, pages 449–454, (February 2014)-- January 14, 2014 ...[Visit Journal] The growth of catalyst-free ZnO nanostructure arrays on silicon (111) substrates by pulsed laser deposition was investigated. Without an underlayer, randomly oriented, micron-scale structures were obtained. Introduction of a c-axis oriented ZnO underlayer resulted in denser arrays of vertically oriented nanostructures with either tapering, vertical-walled or broadening forms, depending on background Ar pressure. Nanostructure pitch seemed to be determined by underlayer grain size while nanostructure widths could be narrowed from ∼100–500 to ∼10–50 nm by a 50 °C increase in growth temperature. A dimpled underlayer topography correlated with the moth-eye type arrays while a more granular surface was linked to vertically walled nanocolumns. Between-wafer reproducibility was demonstrated for both moth-eye and vertical nanocolumn arrays. Broadening nanostructures proved difficult to replicate, however. Full 2 inch wafer coverage was obtained by rastering the target with the laser beam. [reprint (PDF)]
16.	Extended short wavelength infrared heterojunction phototransistors based on type II superlattices Arash Dehzangi , Ryan McClintock, Donghai Wu , Abbas Haddadi, Romain Chevallier , and Manijeh Razeghi Applied Physics Letters 114, 191109-- May 17, 2019 ...[Visit Journal] A two terminal extended short wavelength infrared heterojunction phototransistor based on type-II InAs/AlSb/GaSb on a GaSb substrate is designed, fabricated, and investigated. With the base thickness of 40 nm, the device exhibited a 100% cut-off wavelength of 2.3 λ at 300 K. The saturated peak responsivity value is 320.5 A/W at 300 K, under front-side illumination without any antireflection coating. A saturated optical gain of 245 at 300K was measured. At the same temperature, the device exhibited a collector dark current density (at unity optical gain) and a DC current gain of 7.8 X 10³ A/cm² and 1100, respectively. The device exhibited a saturated dark current shot noise limited specific detectivity of 4.9 X 10¹¹ cm·Hz^½/W at 300 K which remains constant over a broad range of wavelengths and applied biases. [reprint (PDF)]
16.	Demonstration of mid-wavelength infrared nBn photodetectors based on type-II InAs/InAs_1-xSb_x superlattice grown by metal-organic chemical vapor deposition Donghai Wu, Arash Dehzangi, and Manijeh Razeghi Appl. Phys. Lett. 115, 061102-- August 6, 2019 ...[Visit Journal] We report design, growth, and characterization of midwavelength infrared nBn photodetectors based on a type-II InAs/InAs_1-xSb_x superlattice on a GaSb substrate grown by metal-organic chemical vapor deposition. An InAs/AlAs_1-ySb_y/InAs/InAs_1-xSb_x superlattice design was used as the large bandgap electron barrier in the photodetectors. At 150 K, the photodetector exhibits a peak responsivity of 1.23 A/W, corresponding to a quantum efficiency of 41% at an applied bias voltage of −100 mV under front-side illumination, with a 50% cut-off wavelength of 4.6 μm. With an R × A of 356 Ω·cm² and a dark current density of 1.6 × 10⁻⁴ A/cm² under an applied bias of −100 mV at 150 K, the photodetector exhibits a specific detectivity of 1.4 × 10¹¹ cm·Hz^1/2/W. [reprint (PDF)]
16.	MOCVD Growth of ZnO Nanostructures Using Au Droplets as Catalysts V.E. Sandana, D.J. Rogers, F.H. Teherani, R. McClintock, M. Razeghi, H.J. Drouhin, M.C. Clochard, V. Sallett, G. Garry and F. Fayoud SPIE Conference, January 20-25, 2008, San Jose, CA Proceedings – Zinc Oxide Materials and Devices III, Vol. 6895, p. 68950Z-1-6.-- February 1, 2008 ...[Visit Journal] ZnO nanostructures were synthesised by Metal Organic Chemical Vapor Deposition growth on Si (100) and c-Al₂O₃ substrates coated with a 5nm thick layer of Au. The Au coated substrates were annealed in air prior to deposition of ZnO so as to promote formation of Au nanodroplets. The development of the nanodroplets was studied as a function of annealing duration and temperature. Under optimised conditions, a relatively homogeneous distribution of regular Au nanodroplets was obtained. Using the Au nanodroplets as a catalyst, MOCVD growth of ZnO nanostructures was studied. Scanning electron microscopy revealed nanostructures with various forms including commonly observed structures such as nanorods, nanoneedles and nanotubes. Some novel nanostructures were also observed, however, which resembled twist pastries and bevelled-multifaceted table legs. [reprint (PDF)]
16.	Light People: Professor Manijeh Razeghi Hui Wang, and Cun Yu Light Sci Appl 13, 164 ...[Visit Journal] Editorial The sense of light is the first sensation the human body develops. The importance of light is self-evident. However, we all know that the light we can see and perceive covers only a small section of the spectrum. Today, for Light People, we feature a researcher who is committed to exploring different spectral bands of light ranging from deep ultraviolet to terahertz waves and working on quantum semiconductor technology, Prof. Manijeh Razeghi of the Northwestern University in the United States. Known for her quick thinking and witty remarks, Prof. Razeghi is passionate about life and always kind to others. As a scientist, she does not limit her research to a single focus, instead, she works on the entire process from material selection, device design, processing, and manufacturing, all the way to product application. She has a strong passion for education, a commitment unwavered by fame or fortune. For her students, she is both a reliable source of knowledge and a motherly figure with a caring heart. She firmly believes that all things in nature can give her energy and inspiration. In science, she is a true “pioneer” in research and a “miner” of scientific discoveries. She advises young scientists to enjoy and love what they do, and turn their research into their hobby. As a female scientist, she calls on all women to realize their true value and potential. Next, let’s hear from Professor Manijeh Razeghi, a true star who radiates energy and light [reprint (PDF)]
16.	High-responsivity GaInAs/InP Quantum Well Infrared Photodetectors Grown by Low-Pressure Metalorganic Chemical Vapor Deposition M. Erdtmann, A. Matlis, C. Jelen, M. Razeghi, and G. Brown SPIE Conference, San Jose, CA, -- January 26, 2000 ...[Visit Journal] We have studied the dependence of the well doping density in n-type GaInAs/InP quantum well IR photodetectors (QWIPs) grown by low-pressure metalorganic chemical vapor deposition. Three identical GaInAs/InP QWIP structures were grown with well sheet carrier densities of 1x10¹¹ cm^-2, 3x10¹¹ cm^-2, and 10x10¹¹ cm^-2; all three samples had very sharp spectral response at λ equals 9.0 μm. We find that there is a large sensitivity of responsivity, dark current, noise current, and detectivity with the well doping density. Measurements revealed that the lowest-doped samples had an extremely low responsivity relative to the doping concentration while the highest-doped sample had an excessively high dark current relative to doping. The middle-doped sample yielded the optimal results. This QWIP had a responsivity of 33.2 A/W and operated with a detectivity of 3.5x10¹⁰ cm·Hz^½·W^-1 at a bias of 0.75 V and temperature of 80 K. This responsivity is the highest value reported for any QWIP in the (lambda) equals 8-9 &mus;m range. Analysis is also presented explaining the dependence of the measured QWIP parameters to well doping density. [reprint (PDF)]
16.	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)]
16.	Intersubband hole absorption in GaAs-GaInP Quantum Wells grown by Gas Source Molecular Beam Epitaxy J. Hoff, C. Jelen, S. Slivken, E. Michel, O. Duchemin, E. Bigan, and M. Razeghi with G. Brown and S.M. Hegde (Wright Laboratory) Applied Physics Letters 65 (9)-- August 29, 1994 ...[Visit Journal] P-doped GaAs‐GaInP quantum wells have been grown on GaAs substrate by gas source molecular beam epitaxy. Structural quality has been evidenced by x-ray diffraction. A narrow low-temperature photoluminescence full width at half‐maximum has been measured. Strong hole intersubband absorption has been observed at 9 μm, and its dependence on light polarization has been investigated. [reprint (PDF)]
16.	Intermixing of GaInP/GaAs Multiple Quantum Wells C. Francis, M.A. Bradley, P. Boucaud, F.H. Julien and M. Razeghi Applied Physics Letters 62 (2)-- January 11, 1993 ...[Visit Journal] The intermixing of GaInP‐GaAs superlattices induced by a heat treatment is investigated as a function of the annealing temperature and duration. Photoluminescence experiments reveal a large red shift of the effective band gap of the annealed quantum wells thus indicating a dominant self‐diffusion of the group III atoms which is confirmed by secondary ion mass spectroscopic measurements. For long enough annealing durations, the red shift saturates and even decreases due to the competing slower self‐diffusion of the group V atoms. Experiments are well understood based on a simple diffusion model. [reprint (PDF)]
16.	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)]
16.	InAs quantum dot infrared photodetectors on InP by MOCVD W. Zhang, H. Lim, M. Taguchi, A. Quivy and M. Razeghi SPIE Conference, San Jose, CA, Vol. 6127, pp. 61270M -- January 23, 2006 ...[Visit Journal] We report our recent results of InAs quantum dots grown on InP substrate by low-pressure metalorganic chemical vapor deposition (MOCVD) for the application of quantum dot infrared photodetector (QDIP). We have previously demonstrated the first InP-based QDIP with a peak detection wavelength at 6.4 µm and a detectivity of 10¹⁰ cm·Hz^½/W at 77K. Here we show our recent work toward shifting the detection wavelength to the 3-5 µm middlewavelength infrared (MWIR) range. The dependence of the quantum dot on the growth conditions is studied by atomic force microscopy, photoluminescence and Fourier transform infrared spectroscopy. Possible ways to increase the quantum efficiency of QDIPs are discussed. [reprint (PDF)]
16.	AlGaN-based deep UV light emitting diodes with peak emission below 255 nm A. Yasan, R. McClintock, K. Mayes, P. Kung, and M. Razeghi SPIE Conference, Jose, CA, Vol. 5732, pp. 197-- January 22, 2005 ...[Visit Journal] We report on the growth and fabrication of AlGaN-based deep ultraviolet light-emitting diodes (LEDs) with peak emission of below 255 nm. In order to achieve such short wavelength UV LEDs, the Al mole fractions in the device layers should be greater than ~60%. This introdues serious challenges on the growth and doping of Al_xGa_1-xN epilayers. However, with the aid of a high-quality AlN template layer and refinement of the growth conditions we have been able to demonstrate UV LEDs emitting below 255 nm. [reprint (PDF)]
16.	Pressure-induced depopulation of the first excited subband in GaInAs/InP heterojunctions D Gauthier, J C Portal and M Razeghi D Gauthier et al 1989 Semicond. Sci. Technol. 4 218-- December 8, 1988 ...[Visit Journal] Following our previous work on (GalnAs)/(lnP) heterojunctions under hydrostatic pressure we present recent experimental results where the evidence for the total depopulation of the first excited electric subband with pressure is demonstrated. The total electron concentration decreases at a rate of 2.7% kbar”, much higher than in previous experiments. The experimental situation can be fitted with the triangular-well approximation if we both assume the change with pressure of the conduction band discontinuity AE, and the deepening of a deep impurity level with activation energy of the order 160 meV at zero pressure. [reprint (PDF)]
16.	Crystallography of epitaxial growth of wurtzite-type thin films on sapphire substrates P. Kung, C.J. Sun, A. Saxler, H. Ohsato, and M. Razeghi Journal of Applied Physics 75 (9)-- May 1, 1994 ...[Visit Journal] In this article, we present a crystallographic model to describe the epitaxial growth of wurtzite‐type thin films such as gallium nitride (GaN) on different orientations of sapphire (Al2O3) substrates. Through this model, we demonstrate the thin films grown on (00⋅1)Al₂O₃ have a better epilayer‐substrate interface quality than those grown on (01⋅2)Al₂O₃. We also show the epilayer grown on (00⋅1)Al₂O₃ are gallium‐terminated, and both (00⋅1) and (01⋅2) surfaces of sapphire crystals are oxygen‐terminated. [reprint (PDF)]

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