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526.  Lateral Epitaxial Overgrowth of GaN on Sapphire and Silicon Substrates for Ultraviolet Photodetector Applications
M. Razeghi, P. Sandvik, P. Kung, D. Walker, K. Mi, X. Zhang, V. Kumar, J. Diaz, and F. Shahedipour
-- May 1, 2000
527.  High Power InAsSb/InAsSbP Electrical Injection Laser Diodes Emitting Between 3—5 μm
B. Lane, S. Tong, J. Diaz, Z. Wu, and M. Razeghi
-- May 1, 2000
528.  The Development of Nitride-based UV Photodetector
D. Walker and M. Razeghi
-- March 1, 2000
529.  Growth and Characterization of Very Long Wavelength Type-II Infrared Detectors
H. Mohseni, A. Tahraoui, J. Wojkowski, M. Razeghi, W. Mitchel, and A. Saxler
SPIE Conference, San Jose, CA, -- January 26, 2000
We report on the growth and characterization of type-II IR detectors with a InAs/GaSb superlattice active layer in the 15-19 μm wavelength range. The material was grown by molecular beam epitaxy on semi-insulating GaAs substrates. The material was processed into photoconductive detectors using standard photolithography, dry etching, and metalization. The 50 percent cut-off wavelength of the detectors is about 15.5 μm with a responsivity of 90 mA/W at 80 K. The 90 percent-10 percent cut-off energy width of the responsivity is only 17 meV which is an indication of the uniformity of the superlattices. These are the best reported values for type-II superlattices grown on GaAs substrates. reprint
530.  Growth and Characterization of Type-II Non-Equilibrium Photovoltaic Detectors for Long Wavelength Infrared Range
H. Mohseni, J. Wojkowski, A. Tahraoui, M. Razeghi, G. Brown and W. Mitche
SPIE Conference, San Jose, CA, -- January 26, 2000
Growth and characterization of type-II detectors for mid-IR wavelength range is presented. The device has a p-i-n structure is designed to operate in the non-equilibrium mode with low tunneling current. The active layer is a short period InAs/GaSb superlattice. Wider bandgap p-type AlSb and n-type InAs layers are used to facilitate the extraction of both electronics and holes from the active layer for the first time. The performance of these devices were compared to the performance of devices grown at the same condition, but without the AlSb barrier layers. The processed devices with the AlSb barrier show a peak responsivity of about 1.2 A/W with Johnson noise limited detectivity of 1.1 X 1011 cm·Hz½/W at 8 μm at 80 K at zero bias. The details of the modeling, growth, and characterizations will be presented. reprint
531.  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
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·Hz½·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
532.  Growth and Optimization of GaInAsP/InP Material System for Quantum Well Infrared Photodetector Applications
M. Erdtmann, J. Jiang, A. Matlis, A. Tahraoui, C. Jelen, M. Razeghi, and G. Brown
SPIE Conference, San Jose, CA, -- January 26, 2000
Multi-quantum well structures of GaxIn1-xAsyP1-y were grown by metalorganic chemical vapor deposition for the fabrication of quantum well IR photodetectors. The thickness and composition of the wells was determined by high-resolution x-ray diffraction and photoluminescence experiments. The intersubband absorption spectrum of the Ga0.47In0.53As/InP, Ga0.38In0.62As0.80P0.20 (1.55 μm)/InP, and Ga0.27In0.73As0.57P0.43 (1.3 μm))/InP quantum wells are found to have cutoff wavelengths of 9.3 μm, 10.7 micrometers , and 14.2 μm respectively. These wavelengths are consistent with a conduction band offset to bandgap ratio of approximately 0.32. Facet coupled illumination responsivity and detectivity are reported for each composition. reprint
533.  Solar-Blind AlxGa1-xN p-i-n Photodetectors grown on LEO and non-LEO GaN
P. Sandvik, D. Walker, P. Kung, K. Mi, F. Shahedipour, V. Kumar, X. Zhang, J. Diaz, C. Jelen, and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 3948, pp. 265 -- January 26, 2000
The III-Nitride material system is an excellent candidate for UV photodetector applications due to its wide, direct bandgaps and robust material nature. However, despite many inherent material advantages, the III-Nitride material system typically suffers from a large number of extended defects which degrade material quality and device performance. One technique aimed at reducing defect densities in these materials is lateral epitaxial overgrowth (LEO). In this work, we present a preliminary comparison between AlGaN UV, solar-blind p-i-n photodiodes fabricated form LEO GaN and non-LEO GaN. Improvements in both responsivity and rejection ratio are observed, however, further device improvements are necessary. For these, we focus on the optimization of the p- i-n structure and a reduction in contact resistivity to p- GaN and p-AlGaN layers. By improving the structure of the device, GaN p-i-n photodiodes were fabricated and demonstrate 86 percent internal quantum efficiency at 362 nm and a peak to visible rejection ratio of 105. Contact treatments have reduced the contact resistivity to p-GaN and p-AlGaN by over one order of magnitude form our previous results. reprint
534.  LEO of III-Nitride on Al2O3 and Si Substrates
M. Razeghi, P. Kung, P. Sandvik, K. Mi, X. Zhang, V.P. Dravid, J. Freitas, and A. Saxler
SPIE Conference, San Jose, CA, -- January 26, 2000
Lateral epitaxial overgrowth (LEO) has recently become the method of choice to reduce the density of dislocations in heteroepitaxial GaN thin films, and is thus expected to lead to enhanced performance devices. We present here the LEO growth and characterization of GaN films by low pressure metalorganic chemical vapor deposition. Various substrates were used, including basal plane sapphire and oriented Si substrates. The steps in the LEO growth technology will be briefly reviewed. The characterization results will be discussed in detail. The structural, electrical and optical properties of the films were assessed through scanning, atomic and transmission electron microscopy, x-ray diffraction, capacitance-voltage, deep level transient spectroscopy, photoluminescence, and scanning cathodoluminenscence measurements. Single-step and double- step LEO GaN was achieved on sapphire. Similarly high quality LEO grown GaN films were obtained on sapphire and silicon substrates. Clear and dramatic reduction in the density of defects are observed in LEO grown materials using the various characterization techniques mentioned previously. reprint
535.  Ultraviolet Detector Materials and Devices Studied by Femtosecond Nonlinear Optical Techniques
M. Wraback, H. Shen, P. Kung, M. Razeghi, J.C. Carrano, T. Li, and J.C. Campbell
SPIE Conference, San Jose, CA, -- January 26, 2000
Femtosecond nonlinear optical techniques have been employed in the study of carrier dynamics and transport in UV detector materials. Visible femtosecond pulses derived from the signal beam of a 250 kHz regenerative amplifier-pumped optical parametric amplifier were frequency doubled to obtain pulses tunable from 250 nm to 375 nm. Time-resolved reflectivity experiments indicate that the room-temperature carrier lifetime in GaN grown by double lateral epitaxial overgrowth is about 3 times longer than that of GaN grown on sapphire without benefit of this technique. The electron velocity-field characteristics and saturation velocity in GaN have been obtained form time-resolved studies of electroabsorption in a GaN p-i-n diode. The peak steady- state velocity of 1.9x107 cm/s in this device occurs at 225 kV/cm. Time-resolved transmission measurements have been used to monitor ultrafast carrier relaxation phenomena in a thin AlGaN layer with bandgap in the solar blind region of the spectrum. Excitation intensity and wavelength dependent studies of the photoinduced bleaching decays suggest that they are primarily governed by trapping in a high density of sub-bandgap defect levels. reprint
536.  Solar-blind AlGaN photodiodes with very low cutoff wavelength
D. Walker, V. Kumar, K. Mi, P. Sandvik, P. Kung, X.H. Zhang, and M. Razeghi
Applied Physics Letters 76 (4)-- January 24, 2000
We report the fabrication and characterization of AlxGa1–xN photodiodes (x~0.70) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The peak responsivity for –5 V bias is 0.11 A/W at 232 nm, corresponding to an internal quantum efficiency greater than 90%. The device response drops four orders of magnitude by 275 nm and remains at low response for the entire near-ultraviolet and visible spectrum. Improvements were made to the device design including a semitransparent Ni/Au contact layer and a GaN:Mg cap layer, which dramatically increased device response by enhancing the carrier collection efficiency. reprint
537.  Tl incorporation in InSb and lattice contraction of In1-xTlxSb
J.J. Lee and M. Razeghi
Applied Physics Letters 76 (3)-- January 17, 2000
Ternary In1−xTlxSb thin films are grown by low pressure metalorganic chemical vapor deposition in the high In composition region. Infrared photoresponse spectra of the In1−xTlxSb epilayers show a clear shift toward a longer wavelength compared to that of InSb. Tl incorporation is confirmed by Auger electron spectroscopy. In contrast to the theoretical expectation, high resolution x-ray diffraction study reveals that the lattice of the In1−xTlxSb epilayers is contracted by the incorporation of Tl. As more Tl is incorporated, the lattice contraction is observed to increase gradually in the experimental range. A possible origin of this phenomenon is discussed. Our experimental results suggest that the Tl incorporation behavior in In1−xTlxSb differs from that of other group III impurities in III antimonides. reprint
538.  Advanced Semiconductor Lasers in the 3—10 μm Wavelength Range
M. Razeghi
-- January 1, 2000
539.  Future Trends of III-Nitrides Using Lateral Epitaxial Overgrowth
M. Razeghi, P. Kung, P. Sandvik, X. Zhang, K. Mi, D. Walker, V. Kumar, and J. Diaz
-- December 14, 1999
540.  Pulse Autocorrelation Measurements Based on Two- and Three-Photon Conductivity in a GaN Photodiode
A. Streltsov, K.D. Moll, A. Gaeta, P. Kung, D. Walker, and M. Razeghi
Applied Physics Letters 75 (24)-- December 13, 1999
We characterize the performance of a GaN p-i-n photodiode as a nonlinear sensor for second- and third-order femtosecond pulse autocorrelation measurements in the visible and near-infrared regimes, respectively. The two- and three-photon absorption coefficients for GaN are also determined. reprint
541.  Kinetics of Quantum States in Quantum Cascade Lasers: Device Design Principles and fabrication
M. Razeghi
-- October 1, 1999
542.  Uncooled InAs/GaSb Type-II infrared detectors grown on GaAs substrate for the 8–12 μm atmospheric window
H. Mohseni, J. Wojkowski, M. Razeghi, G. Brown, and W. Mitchel
IEEE Journal of Quantum Electronics 35 (7)-- July 1, 1999
The operation of uncooled InAs-GaSb superlattice photodiodes with a cutoff wavelength of λc=8 μm and a peak detectivity of 1.2×108 cm·Hz½/W at zero bias is demonstrated. The detectivity is similar to the best uncooled HgCdTe detectors and microbolometers. However, the R0A product is more than two orders of magnitude higher than HgCdTe and the device is more than four orders of magnitude faster than microbolometers. These features combined with their low 1/f noise and high uniformity make these type-II photodiodes an excellent choice for uncooled high-speed IR imaging arrays reprint
543.  Exploration of Novel InSbBi Alloy for Uncooled Infrared Photodetector Applications
J.J. Lee, J.D. Kim, and M. Razeghi
-- July 1, 1999
544.  Growth and characterization of InGaAs/InGaP quantum dots for mid-infrared photodetectors
S. Kim, M. Erdtmann, and M. Razeghi
-- July 1, 1999
545.  Theoretical and Experimental Analysis of High Power Al-free InGaAsP/GaAs (808 nm) Laser Diodes
H.J. Yi and M. Razeghi
-- July 1, 1999
546.  InAsSb/InAsP strained-layer superlattice injection lasers operating at 4.0 μm grown by metal-organic chemical vapor deposition
B. Lane, Z. Wu, A. Stein, J. Diaz, and M. Razeghi
Applied Physics Letters 74 (23)-- June 7, 1999
We report high power mid-infrared electrical injection operation of laser diodes based on InAsSb/InAsP strained-layer superlattices grown on InAs substrate by metal-organic chemical vapor deposition. The broad-area laser diodes with 100 μm aperture and 1800 μm cavity length demonstrate peak output powers of 546 and 94 mW in pulsed and cw operation respectively at 100 K with a threshold current density as low as 100 A/cm². reprint
547.  Development of High-performance III-Nitride-based Semiconductor Devices
M. Razeghi, P. Kung, D. Walker, E. Monroy, M. Hamilton, and P. Sandvik
-- June 1, 1999
548.  Low-Threshold 7.3 μm Quantum Cascade Lasers Grown by Gas-Source Molecular Beam Epitaxy
S. Slivken, A. Matlis, A. Rybaltowski, Z. Wu and M. Razeghi
Applied Physics Letters 74 (19)-- May 19, 1999
We report low-threshold 7.3 μm superlattice-based quantum cascade lasers. The threshold current density is 3.4 kA/cm² at 300 K and 1.25 kA/cm² at 79 K in pulsed mode for narrow (∼20 μm), 2 mm-long laser diodes. The characteristic temperature (T0) is 210 K. The slope efficiencies are 153 and 650 mW/A at 300 and 100 K, respectively. Power output is in excess of 100 mW at 300 K. Laser far-field intensity measurements give divergence angles of 64° and 29° in the growth direction and in the plane of the quantum wells, respectively. Far-field simulations show excellent agreement with the measured results. reprint
549.  Exciton localization in group-III nitride quantum wells
V.I. Litvinov and M. Razeghi
Physical Review B 59 (15)-- May 15, 1999
Exciton density of states broadened by compositional disorder in the group-III nitride quantum well is calculated. The excitonic photoluminescence linewidth is estimated and related to the material parameters of the alloy for two limiting cases of two-dimensional (2D) and three-dimensional excitons in the quantum well. It is shown that the effect of the compositional fluctuations depends on dimensionality of the exciton: the 2D excitons are more sensitive to the inhomogeneities than 3D ones. The broad near-band-gap energy states distribution for quasi-two-dimensional excitons is consistent with the experimental evidence of the spontaneous and stimulated emissions from excitonic states localized on compositional fluctuations. reprint
550.  Aluminum gallium nitride short-period superlattices doped with magnesium
A. Saxler, W.C. Mitchel, P. Kung and M. Razeghi
Applied Physics Letters 74 (14)-- April 9, 1999
Short-period superlattices consisting of alternating layers of GaN:Mg and AlGaN:Mg were 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. reprint

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