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2.  Tight-binding theory for the thermal evolution of optical band gaps in semiconductors and superlattices
S. Abdollahi Pour, B. Movaghar, and M. Razeghi
American Physical Review, Vol. 83, No. 11, p. 115331-1-- March 15, 2011 ...[Visit Journal]
A method to handle the variation of the band gap with temperature in direct band-gap III–V semiconductors and superlattices using an empirical tight-binding method has been developed. The approach follows closely established procedures and allows parameter variations which give rise to perfect fits to the experimental data. We also apply the tight-binding method to the far more complex problem of band structures in Type-II infrared superlattices for which we have access to original experimental data recently acquired by our group. Given the close packing of bands in small band-gap Type-II designs, k·p methods become difficult to handle, and it turns out that the sp3s* tight-binding scheme is a practical and powerful asset. Other approaches to band-gap shrinkage explored in the past are discussed, scrutinized, and compared. This includes the lattice expansion term, the phonon softening mechanism, and the electron-phonon polaronic shifts calculated in perturbation theory. [reprint (PDF)]
 
2.  Tunability of intersubband absorption from 4.5 to 5.3 µm in a GaN/Al0.2Ga0.8N superlattices grown by metalorganic chemical vapor deposition
N. Péré-Laperne, C. Bayram, L. Nguyen-Thê, R. McClintock, and M. Razeghi
Applied Physics Letters, Vol. 95, No. 13, p. 131109-- September 28, 2009 ...[Visit Journal]
Intersubband (ISB) absorption at wavelengths as long as 5.3 µm is realized in GaN/Al0.2Ga0.8N superlattices grown by metalorganic chemical vapor deposition. By employing low aluminum content Al0.2Ga0.8N barriers and varying the well width from 2.6 to 5.1 nm, ISB absorption has been tuned from 4.5 to 5.3 µm. Theoretical ISB absorption and interband emission models are developed and compared to the experimental results. The effects of band offsets and the piezoelectric fields on these superlattices are investigated. [reprint (PDF)]
 
2.  Quantum Dot Intersubband Photodetectors
C. Jelen, M. Erdtmann, S. Kim, and M. Razeghi
SPIE Conference, San Jose, CA, -- January 22, 2001 ...[Visit Journal]
Quantum dots are recognized as very promising candidates for the fabrication of intersubband photodetectors in the infrared spectral range. At present, material quality is making rapid progress and some devices have been demonstrated. Examples of mid-infrared quantum dot intersubband photodetectors are presented along with device design and data analysis. Nonetheless, the performance of these devices remains less than comparable quantum well intersubband photodetectors due to difficulties in controlling the quantum dot size and distribution during epitaxy. [reprint (PDF)]
 
1.  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 ...[Visit Journal]
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 (PDF)]
 
1.  Use of PLD-grown moth-eye ZnO nanostructures as templates for MOVPE growth of InGaN-based photovoltaics
Dave Rogers, V. E. Sandana, F. Hosseini Teherani, S. Gautier, G. Orsal, T. Moudakir, M. Molinari, M. Troyon, M. Peres, M. J. Soares, A. J. Neves, T. Monteiro, D. McGrouther, J. N. Chapman, H. J. Drouhin, M. Razeghi, and A. Ougazzaden
Renewable Energy and the Environment, OSA Technical Digest paper PWB3, Optical Society of America, (2011)-- November 2, 2011 ...[Visit Journal]
At this time, no abstract is available. Scopus has content delivery agreements in place with each publisher and currently contains 30 million records with an abstract. An abstract may not be present due to incomplete data, as supplied by the publisher, or is still in the process of being indexed. [reprint (PDF)]
 
1.  Spatial Noise and Correctability of Type-II InAs/GaSb Focal Plane Arrays
P.Y. Delaunay and M. Razeghi
IEEE Journal of Quanutm Electronics, April 2010, Vol. 46, No. 4, p. 584-588-- April 1, 2010 ...[Visit Journal]
A long wavelength infrared focal plane array based on Type-II InAs/GaSb superlattices was fabricated and characterized at 80 K. The noise equivalent temperature difference of the array was measured as low as 23 mK (f# = 2), for an integration time of 0.129 ms. The spatial noise of the array was dominated by the nonuniformity of the illumination through the circular aperture. A standard two-point nonuniformity correction improved the inhomogeneity equivalent temperature difference to 16 mK. The correctability just after calibration was 0.6. The long-term stability time was superior to 25 hours. [reprint (PDF)]
 
1.  Noise analysis in type-II InAs/GaSb focal plane arrays
P.Y. Delaunay and M. Razeghi
Journal of Applied Physics, Vol. 106, Issue 6, p. 063110-- September 15, 2009 ...[Visit Journal]
A long wavelength infrared focal plane array based on type-II InAs/GaSb superlattices was fabricated and characterized at 80 K. The noise equivalent temperature difference in the array was measured as low as 23 mK for an integration time of 0.129 ms. The noise behavior of the detectors was properly described by a model based on thermal, shot, read out integrated circuit, and photon noises. The noise of the imager was dominated by photon noise for photon fluxes higher than 1.8×1015 ph·s−1·cm−2. At lower irradiance, the imager was limited by the shot noise generated by the dark current or the noise of the testing system. The superlattice detector did not create 1/f noise for frequencies above 4 mHz. As a result, the focal plane array did not require frequent calibrations. [reprint (PDF)]
 
1.  The effect of doping the M-barrier in very long-wave type-II InAs/GaSb heterodiodes
D. Hoffman, B.M. Nguyen, E.K. Huang, P.Y. Delaunay, M. Razeghi, M.Z. Tidrow and J. Pellegrino
Applied Physics Letters, Vol. 93, No. 3, p. 031107-1-- July 21, 2008 ...[Visit Journal]
A variation on the standard homo-diode Type-II superlattice with an M-barrier between the pi-region and the n-region is shown to suppress the dark currents. By determining the optimal doping level of the M-superlattice, dark current densities of 4.95 mA·cm-2 and quantum efficiencies in excess of 20% have been demonstrated at the moderate reverse bias of 50 mV; allowing for near background-limited performance with a Johnson-noise detectivity of 3.11×1010 Jones at 77 K for a 14.58 µm cutoff wavelength for large area diodes without passivation. This is comparable to values for the state-of-the-art HgCdTe photodiodes. [reprint (PDF)]
 
1.  Research activity on Type-II InAs/GaSb superlattice for LWIR detection and imaging at the Center for Quantum Devices
M. Razeghi and B.M. Nguyen
American Institute of Physics Conference Proceedings Vol. 949, Issue 1, p. 35-42, 6th International Workshop on Information Optics (WIO'07), Reykjavik, Iceland, June 25-30, 2007-- October 24, 2007 ...[Visit Journal]
Type-II superlattice photodetectors have recently experienced significant improvements in both theoretical structure design and experimental realization. Empirical Tight Binding Method was initiated and developed for Type-II superlattice. A new Type-II structure, called M-structure, was introduced and theoretically demonstrated high R0A, high quantum efficiency. Device design and growth condition were optimized to improve the performance. As a result, a 54% quantum efficiency, a 12 Ω·cm2 R0A were achieved for 11 µm cut-off photodetector at 77 K. Effective surface passivation techniques for MWIR and LWIR Type-II superlattice were developed. FPA imaging at MWIR and LWIR were demonstrated with a capability of imaging up to room temperature and 211 K respectively. The noise equivalent temperature difference presented a peak at 50 mK for MWIR FPA at 121 K and 26 mK for LWIR FPA at 81 K. [reprint (PDF)]
 
1.  High-detectivity quantum-dot infrared photodetectors grown by metal-organic chemical-vapor deposition
J. Szafraniec, S. Tsao, W. Zhang, H. Lim, M. Taguchi, A.A. Quivy, B. Movaghar and M. Razeghi
Applied Physics Letters 88 (121102)-- March 20, 2006 ...[Visit Journal]
A mid-wavelength infrared photodetector based on InGaAs quantum dots buried in an InGaP matrix and deposited on a GaAs substrate was demonstrated. Its photoresponse at T=77 K was measured to be around 4.7 μm with a cutoff at 5.5 μm. Due to the high peak responsivity of 1.2 A/W and low dark-current noise of the device, a specific peak detectivity of 1.1 x 1012 cm·Hz½·W−1 was achieved at −0.9 V bias [reprint (PDF)]
 
1.  High-quality visible-blind AlGaN p-i-n photodiodes
E. Monroy, M. Hamilton, D. Walker, P. Kung, F.J. Sanchez, and M. Razeghi
Applied Physics Letters 74 (8)-- February 22, 1999 ...[Visit Journal]
We report the fabrication and characterization of AlxGa1−xN p-i-n photodiodes (0 < x < 0.15) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible rejection of six orders of magnitude with a cutoff wavelength that shifts from 365 to 338 nm. 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. This behavior is justified by the strong frequency dependence of the device capacitance. By an admittance analysis, we conclude that speed is not limited by deep levels, but by substitutional Mg capture and emission time. [reprint (PDF)]
 
1.  Uncooled operation of Type-II InAs/GaSb superlattice photodiodes in the mid- wavelength infrared range
Y. Wei, A. Hood, H. Yau, A. Gin, M. Razeghi, M.Z. Tidrow, V. Natha
Applied Physics Letters, 86 (23)-- June 6, 2005 ...[Visit Journal]
We report high performance uncooled midwavelength infrared photodiodes based on interface-engineered InAs/GaSb superlattice. Two distinct superlattices were designed with a cutoff wavelength around 5 µm for room temperature and 77 K. The device quantum efficiency reached more than 25% with responsivity around 1 A/W. Detectivity was measured around 109 cm·Hz½/W at room temperature and 1.5×1013 cm·Hz½/W at 77 K under zero bias. The devices were without antireflective coating. The device quantum efficiency stays at nearly the same level within this temperature range. Additionally, Wannier–Stark oscillations in the Zener tunneling current were observed up to room temperature. [reprint (PDF)]
 
1.  Amorphous ZnO films grown by room temperature pulsed laser deposition on paper and mylar for transparent electronics applications
D.J. Rogers, V.E. Sandana, F. Hosseini Teherani, R. McClintock, M. Razeghi, and H.J. Drouhin
SPIE Proceedings, San Francisco, CA (January 22-27, 2011), Vol. 7940, p. 79401K-- January 24, 2011 ...[Visit Journal]
Recently, there has been a surge of activity in the development of next-generation transparent thin film transistors for use in applications such as electronic paper and flexible organic light emitting diode panels. Amongst the transparent conducting oxides attracting the most interest at present are Amorphous Oxide Semiconductors (AOS) based on ZnO because they exhibit enhanced electron mobility (μ), superior capacity for processability in air and improved thermodynamic stability compared with conventional covalent amorphous semiconductors and existing AOS. Moreover, they give excellent performance when fabricated at relatively low temperature and can readily be made in large area format. Thus, they are projected to resolve the trade-off between processing temperature and device performance and thereby allow fabrication on inexpensive heatsensitive substrates. For the moment, however, an undesireable post-deposition annealing step at a temperature of about 200ºC is necessary in order to obtain suitable electrical and optical properties. This paper demonstrates the possibility of directly engineering amorphous ZnO with relatively high conductiviy at room temperature on paper and mylar substrates using pulsed laser deposition. [reprint (PDF)]
 
1.  Thin film transistors with wurtzite ZnO channels grown on Si3N4/SiO2/Si (111) substrates by pulsed laser deposition
D.J. Rogers; V.E. Sandana; F. Hosseini Teherani; M. Razeghi
Proc. SPIE 7603, Oxide-based Materials and Devices, 760318 (March 02, 2010)-- March 7, 2010 ...[Visit Journal]
Thin Film Transistors (TFT) were made by growing ZnO on Si3N4/SiO2/Si (111) substrates by pulsed laser deposition. X-ray diffraction and scanning electron microscope studies revealed the ZnO to have a polycrystalline wurtzite structure with a smooth surface, good crystallographic quality and a strong preferential c-axis orientation. Transmission studies in similar ZnO layers on glass substrates showed high transmission over the whole visible spectrum. Electrical measurements of a back gate geometry FET showed an enhancement-mode response with hard saturation, mA range Id and a VON ∼ 0V. When scaled down, such TFTs may be of interest for high frequency applications. [reprint (PDF)]
 
1.  Investigations of ZnO thin films grown on c-Al(2)O(3) by pulsed laser deposition in N(2) + O(2) ambient
D.J. Rogers, D.C. Look, F.H. Teherani, K. Minder, M. Razeghi, A. Largeteau, G. Demazeau, J. Morrod, K.A. Prior, A. Lusson, and S. Hassani
Physica Status Solidi (c), Vol. 5, No. 9, p. 3084-3087-- July 1, 2008 ...[Visit Journal]
ZnO films were deposited on c-Al2O3 using pulsed laser deposition both with and without N2 in the growth ambient. X-ray diffraction revealed poorer crystal quality and surface morphology for one-step growths with N2 in the ambient. A marked improvement in both the crystallographic and surface quality was obtained through use of two-step growths employing nominally undoped ZnO buffer layers prior to growth with N2 in the ambient. All films showed majority n-type conduction in Hall measurements. Post-annealing for 30 minutes at 600 ºC in O2 systematically reduced both the carrier concentration and the conductivity. A base room temperature carrier concentration of ~ 1016 cm-3 was linked to Al diffusing from the substrate. 4.2 K photoluminescence spectra exhibited blue bands associated with the growths having N2 in the ambient. Temperature dependent Hall measurements were consistent with N being incorporated in the films. Processed devices did not, however, show rectifying behavior or electroluminescence. [reprint (PDF)]
 
1.  Thermal imaging based on high-performance InAs/InP quantum-dot infrared photodetector operating at high temperature
M. Razeghi; H. Lim; S. Tsao; H. Seo; W. Zhang
Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS.15-16:[4382251] (2007).-- October 21, 2007 ...[Visit Journal]
We report a room temperature operating and high-performance InAs quantum-dot infrared photodetector on InP substrate and thermal imaging of 320times256 focal plane array based on this device up to 200 K. [reprint (PDF)]
 
1.  Materials characterization of n-ZnO/p-GaN:Mg/c-Al(2)O(3) UV LEDs grown by pulsed laser deposition and metal-organic chemical vapor deposition
D. Rogers, F.H. Teherani, P. Kung, K. Minder, and M. Razeghi
Superlattices and Microstructures-- April 1, 2007 ...[Visit Journal]
n-ZnO/p-GaN:Mg hybrid heterojunctions grown on c-Al2O3 substrates showed 375 nm room temperature electroluminescence. It was suggested that the high materials and interface quality obtained using pulsed laser deposition for the n-ZnO growth and metal–organic chemical vapor deposition for the p-GaN:Mg were key factors enabling the injection of holes and the radiative near band edge recombination in the ZnO. In this paper we present the materials characterization of this structure using x-ray diffraction, scanning electron microscopy and atomic force microscopy. [reprint (PDF)]
 
1.  Investigations of p-type signal for ZnO thin films grown on (100) GaAs substrates by pulsed laser deposition
D.J. Rogers, F. Hosseini Teherani, T. Monteiro, M. Soares, A. Neves, M. Carmo, S. Periera, M.R. Correia, A. Lusson, E. Alves, N.P. Barradas, J.K. Morrod, K.A. Prior, P. Kung, A. Yasan, and M. Razeghi
Phys. Stat. Sol. C, 3 (4)-- March 1, 2006 ...[Visit Journal]
n this work we investigated ZnO films grown on semi-insulating (100) GaAs substrates by pulsed laser deposition. Samples were studied using techniques including X-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy, Raman spectroscopy, temperature dependent photoluminescence, C-V profiling and temperature dependent Hall measurements. [reprint (PDF)]
 
1.  8-13 μm InAsSb heterojunction photodiode operating at near room temperature
J.D. Kim, S. Kim, D. Wu, J. Wojkowski, J. Xu, J. Piotrowski, E. Bigan, and M. Razeghi
Applied Physics Letters 67 (18)-- October 30, 1995 ...[Visit Journal]
p+-InSb/π-InAs1−xSbx/n+-InSb heterojunction photodiodes operating at near room temperature in the 8–13 μm region of infrared (IR) spectrum are reported. A room‐temperature photovoltaic response of up to 13 μm has been observed at 300 K with an x≊0.85 sample. The voltage responsivity‐area product of 3×10−5 V· cm²/W has been obtained at 300 K for the λ=10.6 μm optimized device. This was close to the theoretical limit set by the Auger mechanism, with a detectivity at room temperature of ≊1.5×108 cm ·Hz½/W. [reprint (PDF)]
 
1.  Polarization-free GaN emitters in the ultraviolet and visible spectra via heterointegration on CMOS-compatible Si (100)
C. Bayram, J. Ott, K. T. Shiu, C. W. Cheng, Y. Zhu, J. Kim, D. K. Sadana, M. Razeghi
Proc. SPIE 9370, Quantum Sensing and Nanophotonic Devices XII, 93702F (February 8, 2015); -- February 8, 2015 ...[Visit Journal]
This work presents a new type of polarization-free GaN emitter. The unique aspect of this work is that the ultraviolet and visible emission originates from the cubic phase GaN and the cubic phase InGaN/GaN multi-quantum-wells, respectively. Conventionally, GaN emitters (e.g. light emitting diodes, laser diodes) are wurtzite phase thus strong polarization fields exist across the structure contributing to the “droop” behavior – a phenomenon defined as “the reduction in emitter efficiency as injection current increases”. The elimination of piezoelectric fields in GaN-based emitters as proposed in this work provide the potential for achieving a 100% internal efficiency and might lead to droopfree light emitting diodes. In addition, this work demonstrates co-integration of GaN emitters on cheap and scalable CMOS-compatible Si (100) substrate, which yields possibility of realizing a GaN laser diode uniquely – via forming mirrors along the naturally occurring cubic phase GaN-Si(100) cleavage planes. [reprint (PDF)]
 
1.  Characteristics of high quality p-type AlxGa1-xN/GaN superlattices
A. Yasan, R. McClintock, S.R. Darvish, Z. Lin, K. Mi, P. Kung, and M. Razeghi
Applied Physics Letters 80 (12)-- March 18, 2002 ...[Visit Journal]
Very-high-quality p-type AlxGa1–xN/GaN superlattices have been grown by low-pressure metalorganic vapor-phase epitaxy through optimization of Mg flow and the period of the superlattice. For the superlattice with x = 26%, the hole concentration reaches a high value of 4.2×1018 cm–3 with a resistivity as low as 0.19 Ω · cm by Hall measurement. Measurements confirm that superlattices with a larger period and higher Al composition have higher hole concentration and lower resistivity, as predicted by theory. [reprint (PDF)]
 
1.  Effects of substrate quality and orientation on the characteristics of III-nitride resonant tunneling diodes
Z. Vashaei, C. Bayram, R. McClintock and M. Razeghi
SPIE Proceedings, San Francisco, CA (January 22-27, 2011), Vol 7945, p. 79451A-- January 23, 2011 ...[Visit Journal]
Al(Ga)N/GaN resonant tunneling diodes (RTDs) are grown by metal-organic chemical vapor deposition. The effects of material quality on room temperature negative differential resistance (NDR) behaviour of RTDs are investigated by growing the RTD structure on AlN, GaN, and lateral epitaxial overgrowth GaN templates. This reveals that NDR characteristics of RTDs are very sensitive to material quality (such as surface roughness and dislocations density). The effects of the aluminum content of AlGaN double barriers (DB) and polarization fields on NDR characteristic of AlGaN/GaN RTDs were also investigated by employing low dislocation density c-plane (polar) and m-plane (nonpolar) freestanding GaN substrates. Lower aluminum content in the DB RTD active layer and minimization of dislocations and polarization fields enabled a more reliable and reproducible NDR behaviour at room temperature. [reprint (PDF)]
 
1.  InP-based quantum-dot infrared photodetectors with high quantum efficiency and high temperature imaging
S. Tsao, H. Lim, H. Seo, W. Zhang and M. Razeghi
IEEE Sensors Journal, Vol. 8, No. 6, p. 936-941-- June 1, 2008 ...[Visit Journal]
We report a room temperature operating InAs quantum-dot infrared photodetector grown on InP substrate. The self-assembled InAs quantum dots and the device structure were grown by low-pressure metalorganic chemical vapor depositon. The detectivity was 6 x 1010cm·Hz1/2·W-1 at 150 K and a bias of 5 V with a peak detection wavelength around 4.0 micron and a quantum efficiency of 48%. Due to the low dark current and high responsivity, a clear photoresponse has been observed at room temperature. A 320 x 256 middle wavelength infrared focal plane array operating at temperatures up to 200 K was also demonstrated. The focal plane array had 34 mA/W responsivity, 1.1% conversion efficiency, and noise equivalent temperature difference of 344 mK at 120 K operating temperature. [reprint (PDF)]
 
1.  Dark current suppression in Type-II InAs/GaSb superlattice long wavelength infrared photodiodes with M-structure barrier
B.M. Nguyen, D. Hoffman, P.Y. Delaunay, and M. Razeghi
Applied Physics Letters, Vol. 91, No. 16, p. 163511-1-- October 15, 2007 ...[Visit Journal]
We presented an alternative design of Type-II superlattice photodiodes with the insertion of a mid-wavelength infrared M-structure AlSb/GaSb/InAs/GaSb/AlSb superlattice for the reduction of dark current. The M-structure superlattice has a larger carrier effective mass and a greater band discontinuity as compared to the standard Type-II superlattices at the valence band. It acts as an effective medium that weakens the diffusion and tunneling transport at the depletion region. As a result, a 10.5 µm cutoff Type-II superlattice with 500 nm M-superlattice barrier exhibited a R0A of 200 cm2 at 77 K, approximately one order of magnitude higher than the design without the barrier. The quantum efficiency of such structures does not show dependence on either barrier thickness or applied bias. [reprint (PDF)]
 
1.  High-performance InAs quantum-dot infrared photodetectors grown on InP substrate operating at room temperature
H. Lim, S. Tsao, W. Zhang, and M. Razeghi
Applied Physics Letters, Vol. 90, No. 13, p. 131112-1-- March 26, 2007 ...[Visit Journal]
The authors report a room temperature operating InAs quantum-dot infrared photodetector grown on InP substrate. The self-assembled InAs quantum dots and the device structure were grown by low-pressure metal-organic chemical vapor deposition. The detectivity was 2.8×1011 cm·Hz1/2/W at 120 K and a bias of −5 V with a peak detection wavelength around 4.1 μm and a quantum efficiency of 35%. Due to the low dark current and high responsivity, a clear photoresponse has been observed at room temperature, which gives a detectivity of 6.7×107 cm·Hz1/2/W. [reprint (PDF)]
 

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