Publications by    
Page 1  (21 Items)

1.  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
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
2.  Thermal analysis of buried heterostructure quantum cascade lasers for long-wavelength infrared emission using 2D anisotropic heat-dissipation model
H.K. Lee, K.S. Chung, J.S. Yu and M. Razeghi
Physica Status Solidi (a), Vol. 206, p. 356-362-- February 1, 2009
We have theoretically investigated and compared the thermal characteristics of 10.6 μm InGaAs/InAlAs/InP buried heterostructure (BH) quantum cascade lasers (QCLs) with different heat-sinking configurations by a steady-state heat-transfer analysis. The heat-source densities were obtained from laser threshold power densities measured experimentally under room-temperature continuous-wave mode. The two-dimensional anisotropic heat-dissipation model was used to calculate the temperature distribution, heat flux, and thermal conductance (Gth) inside the device. For good thermal characteristics, the QCLs in the long-wavelength infrared region require the relatively narrow BH structure in combination with epilayer-down bonding due to thick active core/cladding layers and high insulator losses. The single-ridge BH structure results in slightly higher thermal conductance by 2-4% than the double-channel (DC) ridge BH structure. For W = 12 m with 5 μm thick electroplated Au, the single-ridge BH laser with epilayer-down bonding exhibited the highest Gth value of 201.9 W/K cm2, i.e. increased by nearly 36% with respect to the epilayer-up bonded DC ridge waveguide laser. This value is improved by 50% and 62% with respect to the single-ridge BH laser and DC ridge waveguide laser with W = 20 μm in the epilayer-up bonding scheme, respectively. reprint
3.  Comparison of type-II superlattice and HgCdTe infrared detector technologies
Jagmohan Bajaj; Gerry Sullivan; Don Lee; Ed Aifer; Manijeh Razeghi
Proc. SPIE 6542, Infrared Technology and Applications XXXIII, 65420B (May 14, 2007)-- May 14, 2007
Performance of HgCdTe detector technology surpasses all others in the mid-wave and long-wave infrared spectrum. This technology is relatively mature with current effort focused on improving uniformity, and demonstrating increased focal plane array (FPA) functionality. Type-II superlattice (InAs-GaSb and related alloys) detector technology has seen rapid progress over the past few years. The merits of the superlattice material system rest on predictions of even higher performance than HgCdTe and of engineering advantages. While no one has demonstrated Type-II superlattice detectors with performance superior to HgCdTe detectors, the difference in performance between these two technologies is decreasing. In this paper, we review the status and highlight relative merits of both HgCdTe and Type-II superlattice based detector technologies. reprint
4.  Comparison of ultraviolet light-emitting diodes with peak emission at 340 nm grown on GaN substrate and sapphire
A. Yasan, R. McClintock, K. Mayes, S.R. Darvish, H. Zhang, P. Kung, M. Razeghi, S.K. Lee and J.Y. Han
Applied Physics Letters, 81 (12)-- September 16, 2002
Based on AlInGaN/AlInGaN multiquantum wells, we compare properties of ultraviolet light-emitting diodes (LED) with peak emission at 340 nm grown on free-standing hydride vapor phase epitaxially grown GaN substrate and on sapphire. For the LED grown on GaN substrate, a differential resistance as low as 13 Ω and an output power of more than one order of magnitude higher than that of the same structure grown on sapphire are achieved. Due to higher thermal conductivity of GaN, output power of the LEDs saturates at higher injection currents compared to the devices grown on sapphire. reprint
5.  Novel Sb-based Materials for Uncooled Infrared Photodetector Applications
J.J. Lee and M. Razeghi
-- December 1, 2000
6.  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
7.  Exploration of Novel InSbBi Alloy for Uncooled Infrared Photodetector Applications
J.J. Lee, J.D. Kim, and M. Razeghi
-- July 1, 1999
8.  Novel InTlSb Alloy for Uncooled Long-Wavelength Infrared Photodetectors
J.J. Lee, J.D. Kim, and M. Razeghi
-- March 1, 1999
9.  AlxGa1-xN p-i-n Photodiodes on Sapphire Substrates
D. Walker, P. Kung, P. Sandvik, J. Wu, M. Hamilton, I.H. Lee, J. Diaz, and M. Razeghi
SPIE Conference, San Jose, CA, -- January 27, 1999
We report the fabrication and characterization of AlxGa1-xN p-i-n photodiodes (0.05 ≤ to X ≤ 0.30) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible-rejection of about four orders of magnitude with a cutoff wavelength that shifts from 350 nm to 291 nm. They also exhibit a constant responsivity for five decades (30 mW/m² to 1 kW/m²) of optical power density. Using capacitance measurements, the values for the acceptor concentration in the p-AlxGa1-xN region and the unintentional donor concentration in the intrinsic region are found. Photocurrent decays are exponential for high load resistances, with a time constant that corresponds to the RC product of the system. For low load resistances the transient response becomes non-exponential, with a decay time longer than the RC constant. reprint
10.  Schottky MSM Photodetectors on GaN Films Grown on Sapphire by Lateral Epitaxial Overgrowth
P. Kung, D. Walker, P. Sandvik, M. Hamilton, J. Diaz, I.H. Lee and M. Razeghi
SPIE Conference, San Jose, CA, -- January 27, 1999
We report the growth and characterization of Schottky based metal-semiconductor-metal ultraviolet photodetectors fabricated on lateral epitaxially overgrown GaN films. The lateral epitaxial overgrowth of GaN was carried out on basal plane sapphire substrates by low pressure metalorganic chemical vapor deposition and exhibited lateral growth rates more than 5 times as high as vertical growth rates. The spectral responsivity, the dependence on bias voltage, on incident optical power, and the time response of these photodetectors have been characterized. Two detector orientations were investigated: one with the interdigitated finger pattern parallel and the other perpendicular to the underlying SiOx mask stripes. reprint
11.  Growth of InAsSb Alloys on GaAs and Si Substrates for Uncooled Infrared Photodetector Applications
J.D. Kim, H. Mohseni, J.S. Wojkowski, J.J. Lee and M. Razeghi
SPIE Conference, San Jose, CA, -- January 27, 1999
In this paper, we report on the growth and characterization of InAsSb alloys on GaAs and Si substrates for uncooled infrared photodetector applications. The fabrication and characterization of photodetectors from the grown layers are also reported. The photovoltaic and photoconductive devices were grown on (100) GaAs and Si substrates, respectively, using molecular beam epitaxy (MBE). The composition of InAs>sub>1-xSbx layers was 0.95 in both cases and cut-off wavelength of 7-8 μm has been obtained. At 300 K, the photovoltaic detectors on GaAs substrates resulted in a sharp cut-off wavelength of 7.5 μm with a peak responsivity as high as 0.32 V/W at 6.5 micrometer. For the photoconductive detectors on Si substrates, cut-off wavelength of 8 μm has been observed with a responsivity of 6.3x10-2 V/W at 7 μm under an electric field of 420 V/m. reprint
12.  Band-gap narrowing and potential fluctuation in Si-doped GaN
I.H. Lee, J.J. Lee, P. Kung, F.J. Sanchez, and M. Razeghi
Applied Physics Letters 74 (1)-- January 4, 1999
We investigate the optical properties of two sets of Si-doped GaN epitaxial layers with different degree of compensation. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. The photoluminescence peak positions of heavily compensated samples are shifted downward with respect to those of moderately compensated samples, and the down shift becomes larger at higher electron density. Based on analysis of photoluminescence spectra, these prominent behaviors are accounted for by band-edge potential fluctuation associated with inhomogeneous residual impurities. reprint
13.  Uncooled long-wavelength infrared photodetectors using narrow bandgap semiconductors
M. Razeghi, J. Wojkowski, J.D. Kim, H. Mohseni and J.J. Lee
-- October 12, 1998
14.  Room temperature operation of 8-12 μm InSbBi infrared photodetectors on GaAs substrates
J.J. Lee, J.D. Kim, and M. Razeghi
Applied Physics Letters 73 (5)-- August 3, 1998
We report the room temperature operation of 8–12 μm InSbBi long-wavelength infrared photodetectors. The InSbBi/InSb heterostructures were grown on semi-insulating GaAs (001) substrates by low pressure metalorganic chemical vapor deposition. The voltage responsivity at 10.6 μm was about 1.9 mV/W at room temperature and the corresponding Johnson noise limited detectivity was estimated to be about 1.2×106 cm·Hz½/W. The carrier lifetime derived from the voltage dependent responsivity measurements was about 0.7 ns. reprint
15.  Electrical Transport Properties of Highly Doped N-type GaN Epilayers
H.J. Lee, M.G. Cheong, E.K. Suh, and M. Razeghi
SPIE Conference, San Jose, CA, -- January 28, 1998
Temperature-dependent Hall-effects in MOCVD-grown Si-doped GaN epilayers were measured as a function of temperature in the range 10-800 K. The results were satisfactorily analyzed in terms of a two-band model including the (Gamma) and impurity bands at lower temperatures than room. The (Gamma) band electrons are dominant only high temperatures. The ionized impurity scattering is the most important in the (Gamma) band except at very high temperatures. reprint
16.  Exploration of InSbBi for uncooled long-wavelength infrared photodetectors
J.J. Lee and M. Razeghi
-- January 1, 1998
17.  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
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· Hz½/W. The carrier lifetime was estimated to be about 86 ns from the voltage-dependent responsivity measurements. reprint
18.  Schottky barrier heights and conduction-band offsets of In1-xGaxAs1-yPy lattice matched to GaAs
J.K. Lee, Y.H. Cho, B.D. Choe, K.S. Kim, H.I. Jeon, H. Lim and M. Razeghi
Applied Physics Letters 71 (7)-- August 18, 1997
The Schottky barrier heights of Au/In1−xGaxAs1−yPy contacts have been determined as a function of y by the capacitance–voltage and temperature dependent current–voltage characteristics measurements. The barrier height is observed to increase as y is increased for both n- and p-type materials, with a more rapid increase for the p-type material. The compositional variation of the barrier heights for Au/n-In1−xGaxAs1−yPy is found to be identical to that of the conduction-band offsets in In1−xGaxAs1−yPy/GaAs heterojunctions. A possible cause of this phenomenon is also discussed. reprint
19.  Growth and characterization of InSbBi for long wavelength infrared photodetectors
J.J. Lee, J.D. Kim, and M. Razeghi
Applied Physics Letters 70 (24)-- June 16, 1997
The epitaxial growth of InSbBi ternary alloys by low-pressure metalorganic chemical vapor deposition is reported on. X-ray diffraction spectra showed well resolved peaks of InSbBi and InSb films. Bi incorporation was confirmed by energy dispersive x-ray analysis. Photoresponse spectrum up to 9.3 μm which corresponds to 0.13 eV energy band gap has been measured in a sample with Bi composition of 5.8 at.% at 77 K. Electron mobility at room temperature ranges from 44 100 to 4910 cm²/V·s as Bi composition increases. reprint
20.  Sb-based infrared materials and photodetectors for the near room temperature applications
J.D. Kim, E. Michel, H. Mohseni, J. Wojkowski, J.J. Lee and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 2999, pp. 55-- February 12, 1997
We report on the growth of InSb, InAsSb, and InTlSb alloys for infrared photodetector applications. The fabrication and characterization of photodetectors based on these materials are also reported. Both photoconductive and photovoltaic devices are investigated. The materials and detector structures were grown on (100) and (111)B semi-insulating GaAs and GaAs coated Si substrates by low pressure metalorganic chemical vapor deposition and solid source molecular beam epitaxy. Photoconductive detectors fabricated from InAsSb and InTlSb have been operated in the temperature range from 77 K to 300 K. The material parameters for photovoltaic device structures have been optimized through theoretical calculations based on fundamental mechanisms. InSb p-i-n photodiodes with 77 K peak responsivities approximately 103 V/W were grown on Si and (111) GaAs substrates. An InAsSb photovoltaic detector with a composition of x equals 0.85 showed photoresponse up to 13 micrometers at 300 K with a peak responsivity of 9.13 X 10-2 V/W at 8 micrometers . The RoA product of InAsSb detectors has been theoretically and experimentally analyzed. reprint
21.  Infrared Imaging Arrays Using Advanced III-V Materials and technology
M. Razeghi, J.D. Kim, C. Jelen, S. Slivken, E. Michel, H. Mohseni, J.J. Lee, J. Wojkowski, K.S. Kim, H.I. Jeon, and J. X
IEEE Proceedings, Advanced Workshop on Frontiers in Electronics (WOFE), Tenerife, Spain;-- January 6, 1997
Photodetectors operating in the 3-5 and 8-12 μm atmospheric windows are of great importance for applications in infrared (IR) thermal imaging. HgCdTe has been the dominant material system for these applications. However, it suffers from instability and non-uniformity problems over large areas due to high Hg vapor pressure during the material, growth. There has been a lot of interest in the use of heteroepitaxially grown Sb-based alloys, its strained layer superlattices, and GaAs based quantum wells as alternatives to MCT. This interest has been driven by the advanced material growth and processing technology available for the III-V material system reprint

Page 1  (21 Items)