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2.  Substrate emission quantum cascade ring lasers with room temperature continuous wave operation
Y. Bai, S. Tsao, N. Bandyopadhyay, S. Slivken, Q.Y. Lu, and M. Razeghi
SPIE Proceedings, Vol. 8268, p. 82680N-- January 22, 2012 ...[Visit Journal]
We demonstrate room temperature, continuous wave operation of quantum cascade ring lasers around 5 μm with single mode operation up to 0.51 W output power. Single mode operation persists up to 0.4 W. Light is coupled out of the ring cavity through the substrate with a second order distributed feedback grating. The substrate emission scheme allows for epilayer-down bonding, which leads to room temperature continuous wave operation. The far field analysis indicates that the device operates in a high order mode. [reprint (PDF)]
 
2.  InAs/InAs1-XSbx Type-II Superlattices for High-Performance Long-Wavelength Infrared Medical Thermography
Manijeh Razeghi, Abbas Haddadi, Guanxi Chen, Romain Chevallier and Ahn Minh Hoang
ECS Trans. 2015 66(7): 109-116-- June 1, 2015 ...[Visit Journal]
We present the demonstration of a high-performance long-wavelength infrared nBn photodetectors based on InAs/InAs1-xSbx type-II superlattices on GaSb substrate. The photodetector’s 50% cut-off wavelength was ~10 μm at 77K. The photodetector with a 6 μm-thick absorption region exhibited a peak responsivity of 4.47 A/W at 7.9 μm, corresponding to a quantum efficiency of 54% at -90 mV applied bias voltage under front-side illumination and without any anti-reflection coating. With an R×A of 119 Ω·cm² and a dark current density of 4.4×10-4 A/cm² under -90 mV applied bias voltage at 77 K, the photodetector exhibited a specific detectivity of 2.8×1011 Jones. This photodetector opens a new horizon for making infrared imagers with higher sensitivity for medical thermography.
 
2.  High power, continuous wave, quantum cascade ring laser
Y. Bai, S. Tsao, N. Bandyopadhyay, S. Slivken, Q.Y. Lu, D. Caffey, M. Pushkarsky, T. Day and M. Razeghi
Applied Physics Letters, Vol. 99, No. 26, p. 261104-1-- December 26, 2011 ...[Visit Journal]
We demonstrate a quantum cascade ring laser with high power room temperature continuous wave operation. A second order distributed feedback grating buried inside the waveguide provides both in-plane feedback and vertical power outcoupling. Total output power reaches 0.51 W at an emission wavelength around 4.85 μm. Single mode operation persists up to 0.4 W. The far field analysis indicates that the device operates in a high order mode. The magnetic and electric components of the ring-shaped lasing beam are in radial and azimuthal directions, respectively. [reprint (PDF)]
 
2.  High Performance Solar-Blind Ultraviolet Focal Plane Arrays Based on AlGaN
Erdem Cicek, Ryan McClintock, Abbas Haddadi, William A. Gaviria Rojas, and Manijeh Razeghi
IEEE Journal of Quantum Electronics, Vol. 50, Issue 8, p 591-595-- August 1, 2014 ...[Visit Journal]
We report on solar-blind ultraviolet, AlxGa1-x N- based,p-i-n,focal plane array (FPA) with 92% operability. At the peak detection wavelength of 278 nm, 320×256-FP A-pixel showed unbiased peak external quantum efficiency (EQE) and responsivity of 49% and 109 mA/W, respectively, increasing to 66% under 5 volts of reverse bias. Electrical measurements yielded a low-dark current density: <7×10-9A/cm², at FPA operating voltage of 2 volts of reverse bias. [reprint (PDF)]
 
2.  Influence of Residual Impurity Background on the Non-radiative Recombination Processes in High Purity InAs/GaSb superlattice Photodiodes
E.C.F. da Silva, D. Hoffman, A. Hood, B. Nguyen, P.Y. Delaunay and M. Razeghi
Applied Physics Letters, 89 (24)-- December 11, 2006 ...[Visit Journal]
The influence of the impurity background on the recombination processes in type-II InAs/GaSb superlattice photodiodes with a cutoff wavelength of approximately 4.8 μm was investigated by electroluminescence measurements. Using an iterative fitting procedure based on the dependence of the quantum efficiency of the electroluminescence on the injection current, the Auger and Shockley-Read-Hall lifetimes were determined [reprint (PDF)]
 
2.  High-power, room-temperature and continuous-wave operation of distributed-feedback quantum-cascade lasers at λ = 4.8 µm
J.S. Yu, S. Slivken, S.R. Darvish, A. Evans, B. Gokden and M. Razeghi
Applied Physics Letters, 87 (4)-- July 25, 2005 ...[Visit Journal]
The authors present high-power continuous-wave (cw) operation of distributed-feedback quantum-cascade lasers. Continuous-wave output powers of 56 mW at 25 °C and 15 mW at 40 °C are obtained. Single-mode emission near 7.8 µm with a side-mode suppression ratio of >=30 dB and a tuning range of 2.83 cm−1 was obtained between 15 and 40 °C. The device exhibits no beam steering with a full width at half maximum of 27.4° at 25 °C in cw mode. [reprint (PDF)]
 
2.  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)]
 
2.  Substrate removal for high quantum efficiency back side illuminated type-II InAs/GaSb photodetectors
P.Y. Delaunay, B.M. Nguyen, D. Hoffman and M. Razeghi
Applied Physics Letters, Vol. 91, No. 23, p. 231106-- December 3, 2007 ...[Visit Journal]
A substrate removal technique using an InAsSb etch stop layer improves by a factor of 2 the quantum efficiency of back side illuminated type-II InAs/GaSb superlattice photodetectors. After etching of the GaSb substrate with a CrO3 based solution, the quantum efficiency of the diodes presents Fabry-Pérot oscillations averaging at 56%. Due to the confinement of the infrared light inside the devices, the quantum efficiency for certain devices reaches 75% at 8.5 µm. The implementation of this new technique to a focal plane array resulted in a decrease of the integration time from 0.23 to 0.08 ms. [reprint (PDF)]
 
2.  High operability 1024 x 1024 long wavelength Type-II superlattice focal plane array
A. Haddadi, S.R. Darvish, G. Chen, A.M. Hoang, B.M. Nguyen and M. Razeghi
IEEE Journal of Quantum Electronics (JQE), Vol. 48, No. 2, p. 221-228-- February 10, 2012 ...[Visit Journal]
Electrical and radiometric characterization results of a high-operability 1024 x 1024 long wavelength infrared type-II superlattice focal plane array are described. It demonstrates excellent quantum efficiency operability of 95.8% and 97.4% at operating temperatures of 81 K and 68 K, respectively. The external quantum efficiency is 81% without any antireflective coating. The dynamic range is 37 dB at 81 K and increases to 39 dB at 68 K operating temperature. The focal plane array has noise equivalent temperature difference as low as 27 mK and 19 mK at operating temperatures of 81 K and 68 K, respectively, using f/2 optics and an integration time of 0.13 ms. [reprint (PDF)]
 
2.  High differential resistance type-II InAs/GaSb superlattice photodiodes for the long-wavelength infrared
A. Hood, D. Hoffman, B.M. Nguyen, P.Y. Delaunay, E. Michel and M. Razeghi
Applied Physics Letters, 89 (9)-- August 28, 2006 ...[Visit Journal]
Type-II InAs/GaSb superlattice photodiodes with a 50% cutoff wavelength ranging from 11 to 13 μm are presented. Optimization of diffusion limited photodiodes provided superlattice structures for improved injection efficiency in direct injection hybrid focal plane array applications. [reprint (PDF)]
 
2.  High power InAsSb/InPAsSb/InAs mid-infrared lasers
A. Rybaltowski, Y. Xiao, D. Wu, B. Lane, H. Yi, H. Feng, J. Diaz, and M. Razeghi
Applied Physics Letters 71 (17)-- October 27, 1997 ...[Visit Journal]
We demonstrate high-power InAsSb/InPAsSb laser bars (λ ≈ 3.2 μm) consisting of three 100 μm-wide laser stripes of 700 μm cavity length, with peak output power up to 3 W at 90 K, and far-fields for the direction perpendicular to the junction as narrow as 12° full width half maximum. Spectra and far-field patterns of the laser bars are shown to have excellent characteristics for a wide range of operating conditions, suggesting the possibility of even higher light power emission with good beam quality. Joule heating is shown to be the major factor limiting higher power operation. [reprint (PDF)]
 
2.  Solar-blind photodetectors and focal plane arrays based on AlGaN
R. McClintock, M. Razeghi
Proc. SPIE 9555, Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications, 955502-- August 25, 2015 ...[Visit Journal]
III-Nitride material system (AlGaInN) possesses unique optical, electrical and structural properties such as a wide tunable direct bandgap, inherent fast carrier dynamics; good carrier transport properties, high breakdown fields; and high robustness and chemical stability. Recent technological advances in the wide bandgap AlGaN portion of this material system have led to a renewed interest in ultraviolet (UV) photodetectors. These detectors find use in numerous applications in the defense, commercial and scientific arenas such as covert space-to-space communications, early missile threat detection, chemical and biological threat detection and spectroscopy, flame detection and monitoring, UV environmental monitoring, and UV astronomy.1,2,3 Back illuminated detectors operating in the solar blind region are of special interest. Back illumination allows the detector to be hybridized to a silicon read-out integrated circuit, epi-side down, and still collect light through the back of the transparent sapphire substrate. This allows the realization of solar blind focal plane arrays (FPAs) for imaging applications. Solar-blind FPAs are especially important because of the near total absence of any background radiation in this region. In this talk, we will present our recent back-illuminated solar-blind photodetector, mini-array, and FPA results. By systematically optimizing the design of the structure we have realized external quantum efficiencies (EQE) of in excess of 89% for pixel-sized detectors. Based on the absence of any anti-reflection coating, this corresponds to nearly 100% internal quantum efficiency. At the same time, the dark current remains below ~2 × 10-9 A/cm² even at 10 volts of reverse bias. The detector has a very sharp falloff starting at 275 with the UV-solar rejection of better than three orders of magnitude, and a visible rejection ratio is more than 6 orders of magnitude. This high performance photodetector design was then used as the basis of the realization of solar-blind FPA. We demonstrated a 320×256 FPA with a peak detection wavelength of 278nm. The operability of the FPA was better than 92%, and excellent corrected imaging was obtained. [reprint (PDF)]
 
2.  Study of Au coated ZnO nanoarrays for surface enhanced Raman scattering chemical sensing
Gre´gory Barbillon, Vinod E. Sandana,Christophe Humbert, Benoit Be´lier, David J. Rogers, Ferechteh H. Teherani, Philippe Bove Ryan McClintock and Manijeh Razeghid
Cite this: J. Mater. Chem. C, 2017, 5, 3528-- March 20, 2017 ...[Visit Journal]
At present, the simultaneous attainment of good reproducibility and high enhancement factors (EF) are key challenges in the development of surface enhanced Raman scattering (SERS)substrates for improved chemical and biological sensing. SERS substrates are generally based on distributions of metallic nanoparticles/structures with different shapes and architectures which are prepared by either thermal dewetting, precipitation from colloidal suspensions1–4 or advanced (e.g. deep UV or electron beam (EBL)) lithographic techniques.5–9 Although such substrates can exhibit large Raman enhancements, the former two techniques (colloidal and thermal dewetting) give poor SERS reproducibility while deep UV and EBL are too expensive and/or complex for mass production.
 
2.  Recent Advances in LWIR Type-II InAs/GaSb Superlattice Photodetectors and Focal Plane Arrays at the Center for Quantum Devices
M. Razeghi, D. Hoffman, B.M. Nguyen, P.Y. Delaunay, E.K. Huang, M.Z. Tidrow, and V. Nathan
IEEE Proceedings, Vol. 97, No. 6, p. 1056-1066-- June 1, 2009 ...[Visit Journal]
In recent years, Type-II InAs/GaSb superlattice photo-detectors have experienced significant improvements in material quality, structural designs, and imaging applications. They now appear to be a possible alternative to the state-of-the-art HgCdTe (MCT) technology in the long and very long wavelength infrared regimes. At the Center for Quantum Devices, we have successfully realized very high quantum efficiency, very high dynamic differential resistance R0A - product LWIR Type – II InAs/GaSb superlattice photodiodes with efficient surface passivation techniques. The demonstration of high quality LWIR Focal Plane Arrays that were 100 % fabricated in - house reaffirms the pioneer position of this university-based laboratory. [reprint (PDF)]
 
2.  Suppresion of surface leakage in gate controlled Type-II InAs/GaSb mid-Infrared photodetectors
G. Chen, B.M. Nguyen, A.M. Hoang, E.K. Huang, S.R. Darvish and M. Razeghi
SPIE Proceedings, Vol. 8268, p. 826811-- January 22, 2012 ...[Visit Journal]
One of the biggest challenges of improving the electrical performance in Type II InAs/GaSb superlattice photodetector is suppressing the surface leakage. Surface leakage screens important bulk dark current mechanisms, and brings difficulty and uncertainty to the material optimization and bulk intrinsic parameters extraction such as carrier lifetime and mobility. Most of surface treatments were attempted beyond the mid-infrared (MWIR) regime because compared to the bulk performance, surface leakage in MWIR was generally considered to be a minor factor. In this work, we show that below 150 K, surface leakage still strongly affects the electrical performance of the very high bulk performance p-π-M-n MWIR photon detectors. With gating technique, we can effectively eliminate the surface leakage in a controllable manner. At 110K, the dark current density of a 4.7 μm cut-off gated photon diode is more than 2 orders of magnitude lower than the current density in SiO2 passivated ungated diode. With a quantum efficiency of 48%, the specific detecivity of gated diodes attains 2.5 x 1014 cm·Hz1/2/W, which is 3.6 times higher than that of ungated diodes. [reprint (PDF)]
 
2.  Evaluating the size-dependent quantum efficiency loss in a SiO2-Y2O3 hybrid gated type-II InAs/GaSb long-infrared photodetector array
G. Chen , A. M. Hoang , and M. Razeghi
Applied Physics Letters 104 , 103509 (2014)-- March 14, 2014 ...[Visit Journal]
Growing Y2O3 on 20 nm SiO2 to passivate a 11 μm 50% cut-off wavelength long-wavelength infrared type-II superlattice gated photodetector array reduces its saturated gate bias (VGsat ) to −7 V. Size-dependent quantum efficiency (QE) losses are evaluated from 400 μm to 57 μm size gated photodiode. Evolution of QE of the 57 μm gated photodiode with gate bias and diode operation bias reveals different surface recombination mechanisms. At 77 K and VG,sat , the 57 μm gated photodiode exhibits QE enhancement from 53% to 63%, and it has 1.2 × 10−5 A/cm² dark current density at −200 mV, and a specific detectivity of 2.3 × 1012 Jones. [reprint (PDF)]
 
2.  Radiometric characterization of long-wavelength infrared type II strained layer superlattice focal plane array under low-photon irradiance conditions
J. Hubbs, V. Nathan, M. Tidrow, and M. Razeghi
Optical Engineering, Vol. 51, No. 6, p. 064002-1-- June 15, 2012 ...[Visit Journal]
We present the results of the radiometric characterization of an “M” structure long wavelength infrared Type-II strained layer superlattice(SLS) infrared focal plane array (IRFPA) developed by Northwestern University (NWU). The performance of the M-structure SLS IRFPA was radiometrically characterized as a function of photon irradiance, integration time, operating temperature, and detector bias. Its performance is described using standard figures of merit: responsivity, noise, and noise equivalent irradiance. Assuming background limited performance operation at higher irradiances, the detector quantum efficiency for the SLS detector array is approximately 57%. The detector dark density at 80 K is 142 μA∕cm², which represents a factor of seven reduction from previously measured devices. [reprint (PDF)]
 
2.  Surface leakage reduction in narrow band gap type-II antimonide-based superlattice photodiodes
E.K. Huang, D. Hoffman, B.M. Nguyen, P.Y. Delaunay and M. Razeghi
Applied Physics Letters, Vol. 94, No. 5, p. 053506-1-- February 2, 2009 ...[Visit Journal]
Inductively coupled plasma (ICP) dry etching rendered structural and electrical enhancements on type-II antimonide-based superlattices compared to those delineated by electron cyclotron resonance (ECR) with a regenerative chemical wet etch. The surface resistivity of 4×105 Ω·cm is evidence of the surface quality achieved with ICP etching and polyimide passivation. By only modifying the etching technique in the fabrication steps, the ICP-etched devices with a 9.3 µm cutoff wavelength revealed a diffusion-limited dark current density of 4.1×10−6 A/cm2 and a maximum differential resistance at zero bias in excess of 5300 Ω·cm2 at 77 K, which are an order of magnitude better in comparison to the ECR-etched devices. [reprint (PDF)]
 
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.  Broad area photonic crystal distributed feedback quantum cascade lasers emitting 34 W at λ ~ 4.36 μm
B. Gokden, Y. Bai, N. Bandyopadhyay, S. Slivken and M. Razeghi
Applied Physics Letters, Vol. 97, No. 13, p. 131112-1-- September 27, 2010 ...[Visit Journal]
We demonstrate room temperature, high power, single mode, and diffraction limited operation of a two dimensional photonic crystal distributed feedback quantum cascade laser emitting at 4.36 μm. Total peak power up to 34 W is observed from a 3 mm long laser with 400 μm cavity width at room temperature. Far-field profiles have M2 figure of merit as low as 2.5. This device represents a significant step toward realization of spatially and spectrally pure broad area high power quantum cascade lasers. [reprint (PDF)]
 
2.  Demonstration of high performance long wavelength infrared Type-II InAs/GaSb superlattice photodidoe grown on GaAs substrate
S. Abdollahi Pour, B.M. Nguyen, S. Bogdanov, E.K. Huang, and M. Razeghi
Applied Physics Letters, Vol. 95, No. 17, p. 173505-- October 26, 2009 ...[Visit Journal]
We report the growth and characterization of long wavelength infrared type-II InAs/GaSb superlattice photodiodes with a 50% cut-off wavelength at 11 µm, on GaAs substrate. Despite a 7.3% lattice mismatch to the substrate, photodiodes passivated with polyimide exhibit an R0A value of 35 Ω·cm² at 77 K, which is in the same order of magnitude as reference devices grown on native GaSb substrate. With a reverse applied bias less than 500 mV, the dark current density and differential resistance-area product are close to that of devices on GaSb substrate, within the tolerance of the processing and measurement. The quantum efficiency attains the expected value of 20% at zero bias, resulting in a Johnson limited detectivity of 1.1×1011 Jones. Although some difference in performances is observed, devices grown on GaAs substrate already attained the background limit performance at 77 K with a 300 K background and a 2-π field of view. [reprint (PDF)]
 
2.  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)]
 
2.  Demonstration of high performance bias-slectable dual-band short-/mid-wavelength infrared photodetectors based on type-II InAs/GaSb/AlSb superlattices
A.M. Hoang, G. Chen, A. Haddadi and M. Razeghi
Applied Physics Letters, Vol. 102, No. 1, p. 011108-1-- January 7, 2013 ...[Visit Journal]
High performance bias-selectable dual-band short-/mid-wavelength infrared photodetector based on InAs/GaSb/AlSb type-II superlattice with designed cut-off wavelengths of 2 μm and 4 μm was demonstrated. At 150 K, the short-wave channel exhibited a quantum efficiency of 55%, a dark current density of 1.0 × 10−9 A/cm² at −50 mV bias voltage, providing an associated shot noise detectivity of 3.0 × 1013 Jones. The mid-wavelength channel exhibited a quantum efficiency of 33% and a dark current density of 2.6 × 10−5 A/cm² at 300 mV bias voltage, resulting in a detectivity of 4.0 × 1011 Jones. The spectral cross-talk between the two channels was also discussed for further optimization. [reprint (PDF)]
 
2.  Photonic crystal distributed feedback quantum cascade lasers with 12 W output power
Y. Bai, B. Gokden, S.R. Darvish, S. Slivken, and M. Razeghi
Applied Physics Letters, Vol. 95, No. 3-- July 20, 2009 ...[Visit Journal]
We demonstrate room temperature, high power, and diffraction limited operation of photonic crystal distributed feedback (PCDFB) quantum cascade lasers emitting around 4.7 µm. PCDFB gratings with three distinctive periods are fabricated on the same wafer. Peak output power up to 12 W is demonstrated. Lasers with different periods show expected wavelength shifts according to the design. Dual mode spectra are attributed to a purer index coupling by putting the grating layer 100 nm away from the laser core. Single lobed diffraction limited far field profiles are observed. [reprint (PDF)]
 
2.  Demonstration of mid-infrared type-II InAs/GaSb superlattice photodiodes grown on GaAs substrate
B.M. Nguyen, D. Hoffman, E.K. Huang, S. Bogdanov, P.Y. Delaunay, M. Razeghi and M.Z. Tidrow
Applied Physics Letters, Vol. 94, No. 22-- June 8, 2009 ...[Visit Journal]
We report the growth and characterization of type-II InAs/GaSb superlattice photodiodes grown on a GaAs substrate. Through a low nucleation temperature and a reduced growth rate, a smooth GaSb surface was obtained on the GaAs substrate with clear atomic steps and low roughness morphology. On the top of the GaSb buffer, a p+-i-n+ type-II InAs/GaSb superlattice photodiode was grown with a designed cutoff wavelength of 4 μm. The detector exhibited a differential resistance at zero bias (R0A)in excess of 1600 Ω·cm2 and a quantum efficiency of 36.4% at 77 K, providing a specific detectivity of 6 X 1011 cm·Hz½/W and a background limited operating temperature of 100 K with a 300 K background. Uncooled detectors showed similar performance to those grown on GaSb substrates with a carrier lifetime of 110 ns and a detectivity of 6 X 108 cm·Hz½/W. [reprint (PDF)]
 

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