Publications by    
Page 26 of 31:  Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26  27 28 29 30 31  >> Next  (770 Items)

626.  Generalized k·p perturbation theory for atomic-scale superlattices
H. Yi and M. Razeghi
Physical Review B 56 (7)-- August 15, 1997
We present a generalized k⋅p perturbation method that is applicable for atomic-scale superlattices. The present model is in good quantitative agreement with full band theories with local-density approximation, and approaches results of the conventional k⋅p perturbation method (i.e., Kane’s Hamiltonian) with the envelope function approximation for superlattices with large periods. The indirect band gap of AlAs/GaAs superlattices with short periods observed in experiments is explained using this method. reprint
627.  Determination of of Band Gap Energy of Al1-xInxN Grown by Metal Organic Chemical Vapor Deposition in the High Al Composition Regime
K.S. Kim, A. Saxler, P. Kung, M. Razeghi, and K.Y. Lim
Applied Physics Letters 71 (6)-- August 11, 1997
Ternary AlInN was grown by metal–organic chemical-vapor deposition in the high Al composition regime. The band-gap energy of AlInN ternary was measured by optical absorption spectroscopy at room temperature. The band-gap energy of Al0.92In0.08N is 5.26 eV. The potential application of AlInN as a barrier material for GaN is also discussed. reprint
628.  GaN Grown Using Trimethylgallium and Triethylgallium
A. Saxler, P. Kung, X. Zhang, D. Walker, J. Solomon, W.C. Mitchel and M. Razeghi
-- July 1, 1997
629.  GaN Doped with Sulfur
A. Saxler, P. Kung, X. Zhang, D. Walker, J. Solomon, M. Ahoujja, W.C. Mitchel, H.R. Vydyanath, and M. Razeghi
-- July 1, 1997
630.  Electroluminescence of III-Nitride Double Heterostructure Light Emitting Diodes with Silicon and Magnesium Doped InGaN
A. Saxler, K.S. Kim, D. Walker, P. Kung, X. Zhang, G.J. Brown, W.C. Mitchel and M. Razeghi
-- July 1, 1997
631.  Localized Epitaxy for Vertical Cavity Surface Emitting Laser Applications
M. Erdtmann, S. Kim and M. Razeghi
-- July 1, 1997
632.  The Long Wavelength Luminescence Observation from the Self-Organized InGaAs Quantum Dots Grown on (100) GaAs Substrate by Metalorganic Chemical Vapor Deposition
S. Kim, M. Erdtmann, and M. Razeghi
-- July 1, 1997
633.  Structural and Microstructural Characterization of GaN Thin Films and GaN-based Heterostructures Grown on Sapphire Substrates
M. Razeghi, P. Kung, X. Zhang, D. Walker, A. Saxler, K.Y. Lim and K.S. Kim
-- June 30, 1997
634.  Stability of far fields in double heterostructure and multiple quantum well InAsSb/InPAsSb/InAs midinfrared lasers
H. Yi, A. Rybaltowski, J. Diaz, D. Wu, B. Lane, Y. Xiao, and M. Razeghi
Applied Physics Letters 70 (24)-- June 16, 1997
Far fields in perpendicular direction to the junction are investigated in double heterostructure (DH) and multiple quantum well (MQW) midwave-infrared InAsSb/InPAsSb/InAs lasers (λ = 3.2–3.6 μm). Strong broadening of the far fields in the DH lasers was observed with increases in temperature and/or current. On the contrary, MQW lasers with otherwise identical structure exhibit very stable far fields as narrow as 23° for all the operating conditions investigated. Our experiment and theoretical modeling suggest that these different behaviors of far fields in DH and MQW lasers are attributed to the refractive index fluctuation in the InAsSb laser active region. reprint
635.  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
636.  Quantum Hall liquid-to-insulator transition in In1-xGaxAs/InP heterostructures
W. Pan, D. Shahar, D.C. Tsui, H.P. Wei, and M. Razeghi
Physical Review B 55 (23)-- June 15, 1997
We report a temperature- and current-scaling study of the quantum Hall liquid-to-insulator transition in an In1-xGaxAs/InP heterostructure. When the magnetic field is at the critical field Bc, ρxx=0.86h/e². Furthermore, the transport near Bc scales as |B- Bc|T with κ=0.45±0.05, and as |B- Bc|I-b with b=0.23±0.05. The latter can be due to phonon emission in a dirty piezoelectric medium, or can be the consequence of critical behavior near Bc, within which z=1.0±0.1 and ν=2.1±0.3 are obtained from our data. reprint
637.  Study on the effects of minority carrier leakage in InAsSb/InPAsSb double heterostructure
B. Lane, D. Wu, H.J. Yi, J. Diaz, A. Rybaltowski, S. Kim, M. Erdtmann, H. Jeon and M. Razeghi
Applied Physics Letters 70 (11)-- April 17, 1997
InAsxSb1−x/InP1−x−yAsxSby double heterostructures have been grown on InAs substrates by metal-organic chemical vapor deposition. The minority carrier leakage to the cladding layers was studied with photoluminescence measurements on the InAsSb/InPAsSb double heterostructures. A carrier leakage model is used to extract parameters related to the leakage current (diffusion-coefficient and length) from experimental results. Using the obtained parameters, the temperature dependence of the threshold current density of InAsSb/InPAsSb double heterostructure lasers is predicted and compared with experimental results. reprint
638.  AlxGa1-xN (0 ≤ x ≤ 1) Ultraviolet Photodetectors Grown on Sapphire by Metal-organic Chemical-vapor Deposition
D. Walker, X. Zhang, A. Saxler, P. Kung, J. Xu, and M. Razeghi
Applied Physics Letters 70 (8)-- February 24, 1997
AlxGa1–xN (0 ≤ x ≤ 1) ultraviolet photoconductors with cutoff wavelengths from 365 to 200 nm have been fabricated and characterized. The maximum detectivity reached 5.5 × 108 cm·Hz1/2/W at a modulating frequency of 14 Hz. The effective majority carrier lifetime in AlxGa1–xN materials, derived from frequency-dependent photoconductivity measurements, has been estimated to be from 6 to 35 ms. The frequency-dependent noise spectrum shows that it is dominated by Johnson noise at high frequencies for low-Al-composition samples. reprint
639.  AlGaN ultraviolet detectors
M. Razeghi and A. Rogalski,
SPIE Conference, San Jose, CA, -- February 12, 1997
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
640.  Intrinsic AlGaN photodetectors for the entire compositional range
D. Walker, X. Zhang, A. Saxler, P. Kung, J. Xu, and M. Razeghi
SPIE Conference, San Jose, CA, -- February 12, 1997
AlxGa1-xN ultraviolet photoconductors with cut- off wavelengths from 365 nm to 200 nm have been fabricated and characterized. Various characteristics of the devices, such as photoresponse, voltage-dependent responsivity, frequency-dependent responsivity and noise spectral density, were measured and cross-referenced with optical, electrical and structural characteristics of the material to provide information about the mechanisms taking place during detection. The maximum detectivity reached 5.5 X 108 cm·Hz½/W at a modulating frequency of 14 Hz. The effective majority carrier lifetime in AlxGa1-xN materials, derived from frequency-dependent photoconductivity measurements, has been estimated to be from 6 to 35 msec. The frequency-dependent noise-spectrum shows that it is dominated by Johnson-noise at high frequencies for low Al-composition samples. reprint
641.  Very Long Wavelength GaAs/GaInP Quantum Well Infrared Photodetectors
C. Jelen, S. Slivken, G.J. Brown, and M. Razeghi
SPIE Conference, San Jose, CA, -- February 12, 1997
We demonstrate long wavelength quantum well infrared photodetectors with GaAs quantum wells and GaInP barriers grown using gas-source molecular beam epitaxy. Wafers were grown with varying well widths. The optimum well width was 75 angstrom, which resulted in a detection peak at 13 μm and a cutoff wavelength of 15 μm. Dark current measurements of the samples with 15 μm cutoff wavelength show low dark current densities. The dark current characteristics have been investigated as a function of temperature and electron density in the well and compared to a model which takes into account thermionic emission and thermally assisted tunneling. The model is used to extract a saturation velocity of 1.5 x 105 cm/s for electrons. The photoelectron lifetime before recapture has been deduced from this carrier velocity and photoconductive gain measurements. The lifetime is found to be approximately 5 ps. Preliminary focal plane array imaging is demonstrated. reprint
642.  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
643.  Growth models of GaN thin films based on crystal chemistry: Hexagonal and cubic GaN on Si substrates
H. Ohsato and M. Razeghi
-- February 12, 1997
644.  Temperature insensitivity of the Al-free InGaAsP/GaAs lasers for λ = 808 and 908 nm
M. Razeghi, H. Yi, J. Diaz, S. Kim, and M. Erdtmann
SPIE Conference, San Jose, CA; Proceedings 3001-- February 12, 1997
n this work, we present our recent achievements for the reliability of the Al-free lasers at high temperatures and high powers. Laser operations up to 30,000 hours were achieved without any degradation in the lasers characteristics from 7 randomly selected InGaAsP/GaAs diodes for λ = 808 nm. The test were performed for lasers without mirror-coating for optical power of 0.5 to 1 W CW at 50 approximately 60 °C. To the best of our knowledge, this is the first direct demonstration of the extremely high reliability of Al-free diodes operations at high powers and temperatures for periods of time much longer than practical need (approximately 3 years). The characteristics during the tests are discussed in detail. reprint
645.  InAsSbP/InAsSb/InAs Diode Lasers Emitting at 3.2 μm Grown by Metalorganic Chemical Vapor Deposition
D. Wu, E. Kaas, J. Diaz, B. Lane, A. Rybaltowski, H.J. Yi, and M. Razeghi
-- February 1, 1997
646.  Compressively-strained multiple quantum well InAsSb lasers emitting at 3.6 μm grown by metal-organic chemical vapor deposition
B. Lane, D. Wu, A. Rybaltowski, H. Yi, J. Diaz, and M. Razeghi
Applied Physics Letters 70 (4)-- January 27, 1997
A compressively strained InAsSb/InAs multiple quantum-well (MQW) structure was grown by low-pressure metal-organic chemical vapor deposition. Maximum output power (from two facets) up to 1 W with differential efficiency about 70% was obtained from a MQW laser with stripe width of 100 μm and cavity length of 700 μm for emitting wavelength of 3.65 μm at 90 K in pulse mode operation. About 2 times lower threshold current density was obtained from the MQW lasers for a temperature range of 90 to 140 K compared to the double heterostructure lasers grown on the same growth conditions. reprint
647.  Aluminum free GaInP/GaAs Quantum Well Infrared Photodetectors for Long Wavelength Detection
C. Jelen, S. Slivken, J. Hoff, M. Razeghi, and G. Brown
Applied Physics Letters 70 (3)-- January 20, 1997
We demonstrate quantum well infrared photodetectors based on a GaAs/Ga0.51In0.49P superlattice structure grown by gas-source molecular beam epitaxy. Wafers were grown with varying well widths. Wells of 40, 65, and 75 Å resulted in peak detection wavelengths of 10.4, 12.8, and 13.3 μm with a cutoff wavelength of 13.5, 15, and 15.5 μm, respectively. The measured peak and cutoff wavelengths match those predicted by eight band theoretical analysis. Measured dark currents were lower than equivalent GaAs/AlGaAs samples. reprint
648.  InAsSbP/InAsSb/InAs Laser Diodes λ = 3.2 μm) Grown by Low-Pressure Metalorganic Chemical Vapor Deposition
J. Diaz, G. Lukas, D. Wu, S. Kim, M. Erdtmann, E. Kaas, and M. Razeghi
Applied Physics Letters 70 (1)-- January 6, 1997
We report metal–organic chemical-vapor deposition-grown double heterostructure InAsSbP/InAsSb/InAs diode lasers emitting at 3.2 μm operating at temperatures up to 220 K with threshold current density of 40 A/cm² at 77 K and characteristic temperature up to 42 K. Output powers as high as 260 mW in pulse mode and 60 mW in continuous wave operation have been obtained from an uncoated 100 μm stripe-width broad-area laser at 77 K. Comparison with theory shows that there is no significant nonradiative recombination mechanism for these lasers at 77 K. reprint
649.  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
650.  Epitaxial growth models of hexagonal and cubic GaN on (100) Si substrates
H. Ohsato, T. Kato, M. Razeghi, and T. Okuda
-- January 1, 1997

Page 26 of 31:  Prev << 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26  27 28 29 30 31  >> Next  (770 Items)