Center for Quantum Devices - Most Downloaded Journal Articles

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8.	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)]
8.	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)]
8.	High-performance, continuous-wave operation of λ ~ 4.6 μm quantum-cascade lasers above room temperature J.S. Yu, S. Slivken, A. Evans and M. Razeghi IEEE Journal of Quantum Electronics, Vol. 44, No. 8, p. 747-754-- August 1, 2008 ...[Visit Journal] We report the high-performance continuous-wave (CW) operation of 10-μm-wide quantum-cascade lasers (QCLs) emitting at λ ~ 4.6 μm, based on the GaInAs–AlInAs material without regrowth, in epilayer-up and -down bonding configurations. The operational characteristics of QCLs such as the maximum average power, peak output power, CW output power, and maximum CW operating temperature are investigated, depending on cavity length. Also, important device parameters, i.e., the waveguide loss, the transparency current density, the modal gain, and the internal quantum efficiency, are calculated from length-dependent results. For a high-reflectivity (HR) coated 4-mm-long cavity with epilayer-up bonding, the highest maximum average output power of 633 mW is measured at 65% duty cycle, with 469 mW still observed at 100%. The laser exhibits the maximum wall-plug efficiencies of 8.6% and 3.1% at 298 K, in pulsed and CW operatons, respectively. From 298 to 393 K, the temperature dependent threshold current density in pulsed operation shows a high characteristic temperature of 200 K. The use of an epilayer-down bonding further improves the device performance. A CW output power of 685 mW at 288 K is achieved for the 4-micron-long cavity. At 298 K, the output power of 590 mW, threshold current density of 1.52 kA / cm2, and maximum wall-plug efficiency of 3.73% are obtained under CW mode, operating up to 363 K (90 °C). For HR coated 3-micron-long cavities, laser characteristics across the same processed wafer show a good uniformity across the area of 2 x 1 cm², giving similar output powers, threshold current densities, and emission wavelengths. The CW beam full-width at half-maximum of far-field patterns are 25 degree and 46 degree for the parallel and the perpendicular directions, respectively. [reprint (PDF)]
8.	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)]
7.	UVC communication with (Al)Ga₂O₃ photodetectors & a Q-switched solid-state laser including demonstration of a Rayleigh-scattering-based NLOS link D. Rogers, V. Sandana, M. Chamberlin, F. Teherani, S. Prein, and M. Razeghi OPTO (SPIE, 2026), Vol. PC13897 ...[Visit Journal] This work reports solar-blind ultraviolet-C (UVC) optical communication links implemented using epitaxial (Al)Ga₂O₃ metal–semiconductor–metal photodetectors paired with a wavelength-matched, passively Q-switched 213 nm solid-state laser. The photodetectors, originally developed for space-based monitoring of the Herzberg continuum, combine high solar blindness, femtoampere-level dark noise, and robust operation under demanding conditions. Both line-of-sight (LOS) and non-line-of-sight (NLOS) communication geometries are investigated. The detectors exhibit a sharp UVC responsivity peak near 215 nm, a solar-rejection ratio exceeding 2 × 10⁴, and low dark signals enabled by bandgap engineering via aluminum alloying. These characteristics allow LOS communication at distances up to 110 m with sub-20 ms response times, as well as detection of NLOS optical signals at the femtowatt level under near-zero-bias (photovoltaic) operating conditions. For off-axis angles of 15°, the measured NLOS photocurrents are in quantitative agreement with single-scatter Rayleigh predictions, while signals at 45° fall below the detection threshold, consistent with reduced scattering volume and angular dependence. To the authors’ knowledge, this constitutes the first experimental demonstration of Rayleigh-scattering-based NLOS UVC communication using Ga₂O₃ photodetectors, extending prior Ga₂O₃ communication studies beyond pure LOS configurations. The results highlight the potential of Ga₂O₃-based sensors and compact solid-state UVC sources for alignment-tolerant and covert optical communication links in both terrestrial and space -relevant environments. [reprint (PDF)]
7.	AlN/GaN double-barrier resonant tunneling diodes grown by metal-organic chemical vapor deposition C. Bayram, Z. Vashaei and M. Razeghi Applied Physics Letters, Vol. 96, No. 4, p. 042103-1-- January 25, 2010 ...[Visit Journal] AlN/GaN double-barrier resonant tunneling diodes (RTDs) were grown by metal-organic chemical vapor deposition on sapphire. RTDs were fabricated via standard processing steps. RTDs demonstrate a clear negative differential resistance (NDR) at room temperature (RT). The NDR was observed around 4.7 V with a peak current density of 59 kA/cm² and a peak-to-valley ratio of 1.6 at RT. Dislocation-free material is shown to be the key for the performance of GaN RTDs. [reprint (PDF)]
7.	High Power Quantum Cascade Lasers (QCLs) Grown by GasMBE M. Razeghi and S. Slivken Opto-Electronics Review, 11 (2)-- January 1, 2003 ...[Visit Journal] This paper is a brief summary of the technological development and state-of-the-art performance of quantum cascade lasers (QCLs) produced at the Centre for Quantum Devices. Laser design will be discussed, as well as experimental details of device fabrication. Recent work has focused on the development of high peak and average power QCLs emitting at room temperature and above. Scaling of the output is demonstrated by increasing the number of emitting regions in the waveguide core. At λ = 9 µm, over 7 W of peak power has bee demonstrated at room temperature for a single diode, with an average power of 300 mW at 6% duty cycle. At shorter wavelengths, laser development includes the use of highly strain-balanced heterostructures in order to maintain a high conduction band offset and minimize leakage current. At λ = 6 µm, utilizing a high reflective coating and epilayer-down mounting of the laser, we have demonstrated 225 mW of average power from a single facet at room temperature. Lastly, these results are put in the perspective of other reported results and possible future directions are discussed. [reprint (PDF)]
7.	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)]
7.	Type-II Binary Superlattices for Infrared Detector M. Razeghi, H. Mohseni and G.J. Brown Journal of the Korean Physical Society 39-- December 1, 2001 ...[Visit Journal] III-V quantum wells and superlattices based on InAs/GaSb/AlSb, and related compounds have attracted many attentions due to their unique band alignments and physical properties. Recently, novel electronic and optoelectronic heterostructures have been proposed from this material system for hundred gigahertz logic circuits, terahertz transistors, RTDs, infrared lasers, and infrared detectors. In this paper we will describe the ongoing research at the Center for Quantum Devices to develop the theory, modeling, growth, characterization, and device fabrication techniques for this material system. We have demonstrated the rst uncooled infrared detectors from type-II superlattices. The measured detectivity is more than 1 x 10⁸ cm·Hz^½/W at 10.6 μm at room temperature which is higher than the commercially available uncooled photon detectors at similar wavelength. In parallel, we have demonstrated the rst high-performance p-i-n type-II photodiode in the very long wavelength infrared (VLWIR) range operating at T = 80 K. The devices with cuto wavelength of 16 μm showed a responsivity of 3.5 A/W at 80 K leading to a detectivity of 1.51 x 10¹⁰ cm·Hz^½/W. Similar devices with cutoff wavelengths up to 25 μm was demonstrated at 80 K. To enhance this technology further, we plan to move from quantum wells to quantum wire and quantum dots. [reprint (PDF)]
5.	-- November 30, 1999
5.	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.
3.	-- November 30, 1999
3.	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.
2.	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)]
2.	-- November 30, 1999
1.	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)]
1.	-- November 30, 1999
1.	-- November 30, 1999
1.	-- November 30, 1999
1.	-- November 30, 1999

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