Center for Quantum Devices - Most Downloaded Journal Articles

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11.	Electrical Characterization of Al_xGa_1-xN for UV Photodetector Applications A. Saxler, M. Ahoujja, W.C. Mitchel, P. Kung, D. Walker, and M. Razeghi SPIE Conference, San Jose, CA, -- January 27, 1999 ...[Visit Journal] Ultraviolet photodetectors have many military and commercial applications. However, for many of these applications, the photodetectors must be solar blind. This means that the photodetectors must have a cutoff wavelength of less than about 270 nm. Semiconductor based devices would then need energy gaps of over 4.6 eV. In the Al_xGa_1-xN system, the aluminum mole fraction, x, required is over 40%. As the energy gap is increased, doping becomes much more difficult, especially p-type doping. This report is a study of the electrical properties of Al_xGa_1-xN to enable better control of the doping. Magnesium doped p-type Al_xGa_1-xN has been studied using high-temperature Hall effect measurements. The acceptor ionization energy has been found to increase substantially with the aluminum content. Short-period superlattices consisting of alternating layers of GaN:Mg and AlGaN:Mg were also grown by low-pressure organometallic vapor phase epitaxy. The electrical properties of these superlattices were measured as a function of temperature and compared to conventional AlGaN:Mg layers. It is shown that the optical absorption edge can be shifted to shorter wavelengths while lowering the acceptor ionization energy by using short- period superlattice structures instead of bulk-like AlGaN:Mg. Silicon doped n-type films have also been studied. [reprint (PDF)]
11.	Characterization of InTlSb/InSb Grown by Low Pressure Metalorganic Chemical Vapor Deposition on GaAs Substrat Y.H. Choi, P. Staveteig, E. Bigan, and M. Razeghi Journal of Applied Physics 75 (6)-- March 15, 1994 ...[Visit Journal] Optical properties of InTlSb, a new long wavelength infrared material, are investigated. InTlSb/InSb epilayers grown by low‐pressure metal‐organic chemical vapor deposition on semi‐insulating GaAs substrates were characterized using Auger electron spectroscopy and Fourier transform infrared spectroscopy. Auger electron spectra confirm the presence of thallium. Transmission measurements at 77 K indicate an absorption shift from 5.5 μm for InSb up to 8 μm for InTlSb that is confirmed by photoconductivity measurements. [reprint (PDF)]
11.	High Quantum Efficiency Solar-Blind Photodetectors R. McClintock, A. Yasan, K. Mayes, D. Shiell, S. Darvish, P. Kung and M. Razeghi SPIE Conference, Jose, CA, Vol. 5359, pp. 434-- January 25, 2004 ...[Visit Journal] We report AlGaN-based back-illuminated solar-blind p-i-n photodetectors with a record peak responsivity of 150 mA/W at 280 nm, corresponding to a high external quantum efficiency of 68%, increasing to 74% under 5 volts reverse bias. Through optimization of the p-AlGaN layer, we were able to remove the out-of-band negative photoresponse originating from the Schottky-like p-type metal contact, and hence significantly improve the degree of solar-blindness [reprint (PDF)]
11.	Long-Wavelength Infrared Photodetectors Based on InSbBi Grown on GaAs Substrates J.J. Lee, J.D. Kim, and M. Razeghi Applied Physics Letters 71 (16)-- October 20, 1997 ...[Visit Journal] We demonstrate the operation of InSbBi infrared photoconductive detectors grown by low-pressure metalorganic chemical vapor deposition on semi-insulating GaAs substrates. The fabricated photodetector showed a cutoff wavelength of 7.7 μm at 77 K. The responsivity of the InSbBi photodetector at 7 μm was about 3.2 V/W at 77 K. The corresponding Johnson-noise limited detectivity was 4.7×10⁸ cm· Hz^½/W. The carrier lifetime was estimated to be about 86 ns from the voltage-dependent responsivity measurements. [reprint (PDF)]
11.	Simultaneous growth of two different oriented GaN epilayers on (11.0) sapphire (I) morphology and orientation T. Kato, H. Ohsato, T. Okuda, P. Kung, A. Saxler, C.J. Sun, and M. Razeghi Journal of Crystal Growth 173-- January 1, 1997 ...[Visit Journal] Two different oriented (00.1) and (10.0)GaN thin films have been grown simultaneously on (11.0)Al2O3 substrates by low-pressure MOCVD. The crystallinity of the epilayer is not as good as a (00.1) epilayer grown with a single orientation. Moreover, three different morphologies of the GaN epilayers have appeared: hexagonal pyramids for (00.1)GaN and rectangular columns or bow tie shapes for (10.0)GaN epilayer. The epitaxial relationship for in-plane direction between epilayer and the substrates has been determined by precession photographs: [100](GaN) boolean AND [001](Al2O3) = 30' for (00.1)GaN parallel to (11.0)Al2O3, and [001](GaN) boolean AND [001](Al2O3) = 30 degrees 43' for (10.0)GaN parallel to (11.0)(Al2O3). The simultaneous growth with different morphologies is very interesting to crystallographers. Usually, this phenomena is very rare because the growth potential energies of different morphologies are usually different from each other. [reprint (PDF)]
10.	Surface Emitting, Tunable, Mid-Infrared Laser with High Output Power and Stable Output Beam Steven Slivken, Donghai Wu & Manijeh Razeghi Scientific Reports volume 9, Article number: 549-- January 24, 2019 ...[Visit Journal] A reflective outcoupler is demonstrated which can allow for stable surface emission from a quantum cascade laser and has potential for cost-effective wafer-scale manufacturing. This outcoupler is integrated with an amplified, electrically tunable laser architecture to demonstrate high power surface emission at a wavelength near 4.9 μm. Single mode peak power up to 6.7 W is demonstrated with >6 W available over a 90 cm⁻¹ (215 nm) spectral range. A high quality output beam is realized with a simple, single-layer, anti-reflective coating. The beam shape and profile are shown to be independent of wavelength. [reprint (PDF)]
10.	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)]
10.	High Power 0.98 μm GaInAs/GaAs/GaInP Multiple Quantum Well Laser K. Mobarhan, M. Razeghi, G. Marquebielle and E. Vassilaki Journal of Applied Physics 72 (9)-- November 1, 1992 ...[Visit Journal] We report the fabrication of high quality Ga_0.8In_0.2As/GaAs/Ga_0.51In_0.49P multiple quantum well laser emitting at 0.98 μm grown by low pressure metalorganic chemical vapor deposition. Continuous wave operation with output power of 500 mW per facet was achieved at room temperature for a broad area laser with 130 μm width and 300 μm cavity length. This is an unusually high value of output power for this wavelength laser in this material system. The differential quantum efficiency exceeded 75% with excellent homogeneity and uniformity. The characteristic temperature, T₀ was in the range of 120–130 K. [reprint (PDF)]
10.	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)]
10.	Quantum Devices Based on Modern Band Structure Engineering and Epitaxial Technology M. Razeghi Modern Physics Letters B, Vol. 22, No. 24, p. 2343-2371-- September 20, 2008 ...[Visit Journal] Modern band structure engineering is based both on the important discoveries of the past century and modern epitaxial technology. The general goal is to control the behavior of charge carriers on an atomic scale, which affects how they interact with each other and their environment. Starting from the basic semiconductor heterostructure, band structure engineering has evolved into a powerful discipline, employing lower dimensionality to demonstrate new material properties. Several modern technologies under development are used as examples of how this discipline is enabling new types of devices and new functionality in areas with immediate application.
10.	GaN avalanche photodiodes grown on m-plane freestanding GaN substrate Z. Vashaei, E. Cicek, C. Bayram, R. McClintock and M. Razeghi Applied Physics Letters, Vol. 96, No. 20, p. 201908-1-- May 17, 2010 ...[Visit Journal] M-plane GaN avalanche p-i-n photodiodes on low dislocation density freestanding m-plane GaN substrates were realized using metal-organic chemical vapor deposition. High quality homoepitaxial m-plane GaN layers were developed; the root-mean-square surface roughness was less than 1 Å and the full-width-at-half-maximum value of the x-ray rocking curve for (1010) diffraction of m-plane GaN epilayer was 32 arcsec. High quality material led to a low reverse-bias dark current of 8.11 pA for 225 μm² mesa photodetectors prior to avalanche breakdown, with the maximum multiplication gain reaching about 8000. [reprint (PDF)]
9.	Observation of a Spin-Polarization Instability in Tilted Magnetic Fields Koch, S., Haug, R. J., von Klitzing, K. & Razeghi, M. Physica B 184, 76–80 (1993)-- February 1, 1993 ...[Visit Journal] We report evidence for a phase transition between a spin-unpolarized state and a spin-polarized state in a two-dimensional electron gas in tilted magnetic fields. This effect is revealed in the magnetoresistance at mK temperatures, where the coincidence of the spin-resolved Landau levels N = 1 up and N = 0 down completely vanishes in samples of sufficiently high mobility, as predicted in recent theoretical studies. The effect is ascribed to electron-electron interactions. [reprint (PDF)]
9.	Temperature dependence of the dark current and activation energy at avalanche onset of GaN Avalanche Photodiodes M.P. Ulmer, E. Cicek, R. McClintock, Z. Vashaei and M. Razeghi SPIE Proceedings, Vol. 8460, p. 84601G-1-- August 15, 2012 ...[Visit Journal] We report a study of the performance of an avalanche photodiode (APD) as a function of temperature from 564 K to 74 K. The dark current at avalanche onset decreases from 564 K to 74 K by approximately a factor of 125 and from 300 K to 74K the dark current at avalanche offset is reduced by a factor of about 10. The drop would have been considerably larger if the activation energy at avalanche onset (Ea) did not also decrease with decreasing temperature. These data give us insights into how to improve the single-photon counting performance of a GaN based ADP. [reprint (PDF)]
7.	Quantum cascade laser: A tool for trace chemical detection Allan J. Evans; Manijeh Razeghi American Filtration and Separations Society - 20th Annual Conference and Exposition of the American Filtration and Separations Society 2:914-923 (2007)-- March 26, 2007 Laser-based trace chemical sensors are highly desired to enhance pollution filtering, health and safety monitoring, and filter efficiency monitoring for industrial processes. Limitations of current monitoring and sensing techniques are discussed and the benefits of mid-infrared spectroscopy using novel Quantum Cascade semiconductor Lasers (QCLs) are presented. These new techniques promise inexpensive, miniaturized sensors, capable of remote detection of trace chemicals in liquids, solids, and gasses with levels less than 1 part-per-billion. Applications of these techniques are discussed and the most recent developments of application-ready high power (> 100 mW), continuous-wave, mid-infrared QCLs operating above room temperature with lifetimes exceeding 12,000 hours are presented.
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