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2.  Active and passive infrared imager based on short-wave and mid-wave type-II superlattice dual-band detectors
E.K. Huang, A. Haddadi, G. Chen, A.M. Hoang, and M. Razeghi
Optics Letters, Vol. 38, no. 1, p. 22-24-- January 1, 2013 ...[Visit Journal]
A versatile dual-band detector capable of active and passive use is demonstrated using short-wave (SW) and midwave(MW) IR type-II superlattice photodiodes. A bilayer etch-stop scheme is introduced for back-side-illuminated detectors, which enhanced the external quantum efficiency both in the SWIR and MWIR spectral regions. Temperature-dependent dark current measurements of pixel-sized 27 μm detectors found the dark current density to be ~1 × 10-5 A/cm² for the ∼4.2 μm cutoff MWIR channel at 140 K. This corresponded to a reasonable imager noise equivalent difference in temperature of ∼49 mK using F∕2.3 optics and a 10 ms integration time (tint), which lowered to ∼13 mK at 110 K using tint  30 ms, illustrating the potential for high-temperature operation. The SWIR channel was found to be limited by readout noise below 150 K. Excellent imagery from the dual-band imager exemplifying pixel coincidence is shown. [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.  Phase-matched optical second-harmonic generation in GaN and AlN slab waveguides
D.N. Hahn, G.T. Kiehne, G.K.L. Wong, J.B. Ketterson, P. Kung, A. Saxler and M. Razeghi
Journal of Applied Physics 85 (5)-- March 1, 1999 ...[Visit Journal]
Phase-matched optical second-harmonic (SH) generation was observed in GaN and AlN slab waveguides. Phase matching was achieved by waveguide modal dispersion. By tuning the output wavelength of an optical parametric amplifier, several phased-matched SH peaks were observed in the visible spectrum covering blue to red wavelengths. The peak positions are in agreement with the values calculated using the dispersive refractive indices of the film and substrate materials. [reprint (PDF)]
 
2.  Recent progress of widely tunable, CW THz sources based QCLs at room temperature
Manijeh Razeghi
Terahertz Science and Technology, Vol.10, No.4, pp. 87-151-- December 7, 2017 ...[Visit Journal]
The THz spectral region is of significant interest to the scientific community, but is one of the hardest regions to access with conventional technology. A wide range of compelling new applications are initiating a new revolution in THz technology, especially with regard to the development of compact and versatile devices for THz emission and detection. In this article, recent advances with regard to III-V semiconductor optoelectronics are explored with emphasis on how these advances will lead to the next generation of THz component technology [reprint (PDF)]
 
2.  Room temperature continuous wave operation of quantum cascade lasers with watt-level optical power
Y. Bai, S.R. Darvish, S. Slivken, W. Zhang, A. Evans, J. Nguyen and M. Razeghi
Applied Physics Letters, Vol. 92, No. 10, p. 101105-1-- March 10, 2008 ...[Visit Journal]
We demonstrate quantum cascade lasers at an emitting wavelength of 4.6 µm, which are capable of room temperature, high power continuous wave (cw) operation. Buried ridge geometry with a width of 9.8 µm was utilized. A device with a 3 mm cavity length that was epilayer-down bonded on a diamond submount exhibited a maximum output power of 1.3 W at room temperature in cw operation. The maximum output power at 80 K was measured to be 4 W, with a wall plug efficiency of 27%. [reprint (PDF)]
 
2.  Low irradiance background limited type-II superlattice MWIR M-barrier imager
E.K. Huang, S. Abdollahi Pour, M.A. Hoang, A. Haddadi, M. Razeghi and M.Z. Tidrow
OSA Optics Letters (OL), Vol. 37, No. 11, p. 2025-2027-- June 1, 2012 ...[Visit Journal]
We report a type-II superlattice mid-wave infrared 320 × 256 imager at 81 K with the M-barrier design that achieved background limited performance (BLIP) and ∼99%operability. The 280 K blackbody’s photon irradiance was limited by an aperture and a band-pass filter from 3.6 μm to 3.8 μm resulting in a total flux of ∼5 × 1012 ph·cm−2·s−1. Under these low-light conditions, and consequently the use of a 13.5 ms integration time, the imager was observed to be BLIP thanks to a ∼5 pA dark current from the 27 μm wide pixels. The total noise was dominated by the photon flux and read-out circuit which gave the imager a noise equivalent input of ∼5 × 1010 ph·cm−2·s−1 and temperature sensitivity of 9 mK with F∕2.3 optics. Excellent imagery obtained using a 1-point correction alludes to the array’s uniform responsivity. [reprint (PDF)]
 
2.  High speed type-II superlattice based photodetectors transferred on sapphire
Arash Dehzangi, Ryan McClintock, Donghai Wu, Jiakai Li, Stephen Johnson, Emily Dial and Manijeh Razeghi
Applied Physics Express, Volume 12, Number 11-- October 3, 2019 ...[Visit Journal]
We report the substrate transfer of InAs/GaSb/AlSb based type-II superlattice (T2SL) e-SWIR photodetector from native GaSb substrates to low loss sapphire substrate in order to enhance the frequency response of the device. We have demonstrated the damage-free transfer of T2SL-based thin-films to sapphire substrate using top–down processing and a chemical epilayer release technique. After transfer the −3 dB cut-off frequency increased from 6.4 GHz to 17.2 GHz, for 8 μm diameter circular mesas under -15 V applied bias. We also investigated the cut-off frequency verses applied bias and lateral scaling to assess the limitations for even higher frequency performance. Direct Link [reprint (PDF)]
 
2.  Toward realization of small-size dual-band long-wavelength infrared photodetectors based on InAs/GaSb/AlSb type-II superlattices
Romain Chevallier, Abbas Haddadi, Manijeh Razeghi
Solid-State Electronics 136, pp. 51-54-- June 20, 2017 ...[Visit Journal]
In this study, we demonstrate 12 × 12 µm² high-performance, dual-band, long-wavelength infrared (LWIR) photodetectors based on InAs/GaSb/AlSb type-II superlattices. The structure consists of two back-to-back heterojunction photodiodes with 2 µm-thick p-doped absorption regions. High quality dry etching combined with SiO2 passivation results in a surface resistivity value of 7.9 × 105 Ω·cm for the longer (red) channel and little degradation of the electrical performance. The device reaches dark current density values of 4.5 × 10−4 A/cm² for the longer (red) and 1.3 × 10−4 A/cm² for the shorter (blue) LWIR channels at quantum efficiency saturation. It has 50% cut-off wavelengths of 8.3 and 11.2 µm for the blue and red channel, respectively, at 77 K in back-side illumination configuration and exhibits quantum efficiencies of 37% and 29%, respectively. This results in specific detectivity values of 2.5 × 1011 cm·Hz½/W and 1.3 × 1011 cm·Hz½/W at 77 K. [reprint (PDF)]
 
2.  Background limited performance of long wavelength infrared focal plane arrays fabricated from M-structure InAs-GaSb superlattices
P.Y. Delaunay, B.M. Nguyen, D. Hoffman, E.K. Huang, and M. Razeghi
IEEE Journal of Quantum Electronics, Vol. 45, No. 2, p. 157-162.-- February 1, 2009 ...[Visit Journal]
The recent introduction of a M-structure design improved both the dark current and R0A performances of Type-II InAs-GaSb photodiodes. A focal plane array fabricated with this design was characterized at 81 K. The dark current of individual pixels was measured between 1.1 and 1.6 nA, 7 times lower than previous superlattice FPAs. This led to a higher dynamic range and longer integration times. The quantum efficiency of detectors without antireflective coating was 74%. The noise equivalent temperature difference reached 23 mK, limited only by the performance of the testing system and the read out integrated circuit. Background limited performances were demonstrated at 81 K for a 300 K background. [reprint (PDF)]
 
2.  Gain and recombination dynamics of quantum-dot infrared photodetectors
H. Lim, B. Movaghar, S. Tsao, M. Taguchi, W. Zhang, A.A. Quivy, and M. Razeghi
Physical Review B, 74 (20)-- November 15, 2006 ...[Visit Journal]
In this paper we present a theory of diffusion and recombination in QDIPs which is an attempt to explain the recently reported values of gain in these devices. We allow the kinetics to encompass both the diffusion and capture rate limited regimes of carrier relaxation using rigorous random walk and diffusion methods. The photoconductive gains are calculated and compared with the experimental values obtained from InGaAs/InGaP/GaAs and InAs/InP QDIPs using the generation-recombination noise analysis. [reprint (PDF)]
 
2.  Growth and Characterization of Long-Wavelength Infrared Type-II Superlattice Photodiodes on a 3-in GaSb Wafer
B.M. Nguyen, G. Chen, M.A. Hoang, and M. Razeghi
IEEE Journal of Quantum Electronics (JQE), Vol. 47, No. 5, May 2011, p. 686-690-- May 11, 2011 ...[Visit Journal]
We report the molecular beam epitaxial growth and characterization of high performance Type-II superlattice photodiodes on 3” GaSb substrates for long wavelength infrared detection. A 7.3 micron thick device structure shows excellent structural homogeneity via atomic force microscopy and x-ray diffraction characterization. Optical and electrical measurements of photodiodes reveal not only the uniformity of the Type-II superlattice material but also of the fabrication process. Across the wafer, at 77 K, photodiodes with a 50% cut-off wavelength of 11 micron exhibit more than 45% quantum efficiency, and a dark current density of 1.0 x 10-4 A/cm² at 50 mV, resulting in a specific detectivity of 6x1011 cm·Hz1/2/W. [reprint (PDF)]
 
2.  New design strategies for multifunctional and inexpensive quantum cascade lasers
Steven Slivken; Manijeh Razeghi
Proc. SPIE 10926, Quantum Sensing and Nano Electronics and Photonics XVI, 1092611-- February 1, 2019 ...[Visit Journal]
This manuscript describes some of the new advances in active mid-infrared photonic integrated circuits enabled by new quantum cascade laser technologies. This includes monolithic beam steering which was achieved via the integration of a widely tunable QCL and a tapered grating outcoupler. A record 17.9 degrees of steering with a low divergence beam (0.5 degrees) was achieved. In addition, the use of surface emitting architectures is proposed as a means to reduce the manufacturing cost of next-generation QCLs. A reflective outcoupler is demonstrated which can allow for stable surface emission from a quantum cascade laser and has potential for cost-effective wafer-scale manufacturing. This outcoupler is integrated with an amplified, electrically tunable laser architecture to demonstrate high power surface emission at a wavelength near 4.9 μm. Single mode peak power up to 6.7 W is demonstrated with >6 W available over a 90 cm−1 (215 nm) spectral range. All of this is achieved while maintaining a high quality output beam, similar to a standard edge emitter. [reprint (PDF)]
 
2.  High-power, continuous-operation intersubband laser for wavelengths greater than 10 micron
S. Slivken, A. Evans, W. Zhang and M. Razeghi
Applied Physics Letters, Vol. 90, No. 15, p. 151115-1-- April 9, 2007 ...[Visit Journal]
In this letter, high-power continuous-wave emission (>100 mW) and high temperature operation (358 K) at a wavelength of 10.6 µm is demonstrated using an individual diode laser. This wavelength is advantageous for many medium-power applications previously reserved for the carbon dioxide laser. Improved performance was accomplished using industry-standard InP-based materials and by careful attention to design, growth, and fabrication limitations specific to long-wave infrared semiconductor lasers. The main problem areas are explored with regard to laser performance, and general steps are outlined to minimize their impact. [reprint (PDF)]
 
2.  Geiger-mode operation of back-illuminated GaN avalanche photodiodes
J. L. Pau, R. McClintock, K. Minder, C. Bayram, P. Kung, M. Razeghi, E. Muñoz, and D. Silversmith
Applied Physics Letters, Vol. 91, No. 04, p. 041104 -1-- July 23, 2007 ...[Visit Journal]
We report the Geiger-mode operation of back-illuminated GaN avalanche photodiodes fabricated on transparent AlN templates specifically for back illumination in order to enhance hole-initiated multiplication. The spectral response in Geiger-mode operation was analyzed under low photon fluxes. Single photon detection capabilities were demonstrated in devices with areas ranging from 225 to 14,063 µm2. Single photon detection efficiency of 20% and dark count rate < 10 kHz were achieved in the smallest devices. [reprint (PDF)]
 
2.  Optical Coatings by ion-beam sputtering deposition for long-wave infrared quantum cascade lasers
J. Nguyen, J.S. Yu, A. Evans, S. Slivken and M. Razeghi
Applied Physics Letters, 89 (11)-- September 11, 2006 ...[Visit Journal]
The authors report on the development of high-reflection and multilayer antireflection coatings using ion-beam sputtering deposition for long-wave infrared (λ~9.4 μm) quantum cascade lasers. A metallic high-reflection coating structure using Y2O3 and Au is demonstrated to achieve a high reflectance of 96.70%, and the use of a multilayer anti-reflection coating structure using PbTe and ZnO is demonstrated to achieve a very low reflectance of 1.64%. [reprint (PDF)]
 
2.  Room temperature continuous wave operation of λ ~ 3-3.2 μm quantum cascade lasers
N. Bandyopadhyay, Y. Bai, S. Tsao, S. Nida, S. Slivken and M. Razeghi
Applied Physics Letters, Vol. 101, No. 24, p. 241110-1-- December 10, 2012 ...[Visit Journal]
We demonstrate quantum cascade lasers emitting at wavelengths of 3–3.2 μm in the InP-based material system. The laser core consists of GaInAs/AlInAs using strain balancing technique. In room temperature pulsed mode operation, threshold current densities of 1.66 kA∕cm² and 1.97 kA∕cm², and characteristic temperatures (T0) of 108 K and 102 K, are obtained for the devices emitting at 3.2 μm and 3 μm, respectively. Room temperature continuous wave operation is achieved at both wavelengths. [reprint (PDF)]
 
2.  Study of Phase Transition in MOCVD Grown Ga2O3 from κ to β Phase by Ex Situ and In Situ Annealing
Junhee Lee, Honghyuk Kim, Lakshay Gautam, Kun He, Xiaobing Hu, Vinayak P. Dravid and Manijeh Razeghi
Photonics 2021, 8, 17. https://doi.org/10.3390/ photonics8010017 ...[Visit Journal]
We report the post-growth thermal annealing and the subsequent phase transition of Ga2O3 grown on c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD). We demonstrated the post-growth thermal annealing at temperatures higher than 900 °C under N2 ambience, by either in situ or ex situ thermal annealing, can induce phase transition from nominally metastable κ- to thermodynamically stable β-phase. This was analyzed by structural characterizations such as high-resolution scanning transmission electron microscopy and x-ray diffraction. The highly resistive as-grown Ga2O3 epitaxial layer becomes conductive after annealing at 1000 °C. Furthermore, we demonstrate that in situ annealing can lead to a crack-free β-Ga2O3. [reprint (PDF)]
 
2.  Scaling in back-illuminated GaN avalanche photodiodes
K. Minder, J.L. Pau, R. McClintock, P. Kung, C. Bayram, M. Razeghi and D. Silversmith
Applied Physics Letters, Vol. 91, No. 7, p. 073513-1-- August 13, 2007 ...[Visit Journal]
Avalanche p-i-n photodiodes of various mesa areas were fabricated on AlN templates for back illumination for enhanced performance through hole-initiated multiplication, and the effects of increased area on device performance were studied. Avalanche multiplication was observed in mesa sizes up to 14,063 µm^2 under linear mode operation. Uniform gain and a linear increase of the dark current with area were demonstrated. [reprint (PDF)]
 
2.  Solar-blind avalanche photodiodes
R. McClintock, K. Minder, A. Yasan, C. Bayram, F. Fuchs, P. Kung and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 6127, pp. 61271D-- January 23, 2006 ...[Visit Journal]
There is a need for semiconductor based UV photodetectors to support avalanche gain in order to realize better performance and more effectively compete with existing photomultiplier tubes. However, there are numerous technical issues associated with the realization of high-quality solar-blind avalanche photodiodes (APDs). In this paper, APDs operating at 280 nm, within the solar-blind region of the ultraviolet spectrum, are investigated. [reprint (PDF)]
 
1.  Review of high power frequency comb sources based on InP From MIR to THZ at CQD
Manijeh Razeghi, Quanyong Lu, Donghai Wu, Steven Slivken
Event: SPIE Optical Engineering + Applications, 2018, San Diego, California, United States-- September 14, 2018 ...[Visit Journal]
We present the recent development of high performance compact frequency comb sources based on mid-infrared quantum cascade lasers. Significant performance improvements of our frequency combs with respect to the continuous wave power output, spectral bandwidth, and beatnote linewidth are achieved by systematic optimization of the device's active region, group velocity dispersion, and waveguide design. To date, we have demonstrated the most efficient, high power frequency comb operation from a free-running room temperature continuous wave (RT CW) dispersion engineered QCL at λ~5-9 μm. In terms of bandwidth, the comb covered a broad spectral range of 120 cm−1 with a radio-frequency intermode beatnote spectral linewidth of 40 Hz and a total power output of 880 mW at 8 μm and 1 W at ~5.0 μm. The developing characteristics show the potential for fast detection of various gas molecules. Furthermore, THz comb sources based on difference frequency generation in a mid-IR QCL combs could be potentially developed. [reprint (PDF)]
 
1.  Characterization of ZnO thin films grown on c-sapphire by pulsed laser deposition as templates for regrowth of zno by metal organic chemical vapor deposition
D. J. Rogers ; F. Hosseini Teherani ; C. Sartel ; V. Sallet ; F. Jomard ; P. Galtier ; M. Razeghi
Proc. SPIE 7217, Zinc Oxide Materials and Devices IV, 72170F (February 17, 2009)-- February 17, 2009 ...[Visit Journal]
The use of ZnO template layers grown Pulsed Laser Deposition (PLD) has been seen to produce dramatic improvements in the surface morphology, crystallographic quality and optical properties of ZnO layers grown on c-sapphire substrates by Metal Organic Chemical Vapor Deposition. This paper provides complementary details on the PLD-grown ZnO template properties. [reprint (PDF)]
 
1.  Type-II InAs/GaSb photodiodes and focal plane arrays aimed at high operating temperatures
M. Razeghi, S. Abdollahi Pour, E.K. Huang, G. Chen, A. Haddadi, and B.M. Nguyen
Opto-Electronics Review (OER), Vol. 19, No. 3, June 2011, p. 46-54-- June 1, 2011 ...[Visit Journal]
Recent efforts to improve the performance of type-II InAs/GaSb superlattice photodiodes and focal plane arrays (FPA) have been reviewed. The theoretical bandstructure models have been discussed first. A review of recent developments in growth and characterization techniques is given. The efforts to improve the performance of MWIR photodiodes and focal plane arrays (FPAs) have been reviewed and the latest results have been reported. It is shown that these improvements has resulted in background limited performance (BLIP) of single element photodiodes up to 180 K. FPA shows a constant noise equivalent temperature difference (NEDT) of 11 mK up to 120 K and it shows human body imaging up to 170 K. [reprint (PDF)]
 
1.  High performance long wavelength infrared mega-pixel focal plane array based on type-II superlattices
P. Manurkar, S.R. Darvish, B.M. Nguyen, M. Razeghi and J. Hubbs
Applied Physics Letters, Vol. 97, No 19, p. 193505-1-- November 8, 2010 ...[Visit Journal]
A large format 1k × 1k focal plane array (FPA) is realized using type-II superlattice photodiodes for long wavelength infrared detection. Material growth on a 3 in. GaSb substrate exhibits a 50% cutoff wavelength of 11 μm across the entire wafer. The FPA shows excellent imaging. Noise equivalent temperature differences of 23.6 mK at 81 K and 22.5 mK at 68 K are achieved with an integration time of 0.13 ms, a 300 K background and f/4 optics. We report a dark current density of 3.3×10−4 A·cm−2 and differential resistance-area product at zero bias R0A of 166 Ω·cm² at 81 K, and 5.1×10−5 A·cm−2 and 1286 Ω·cm², respectively, at 68 K. The quantum efficiency obtained is 78%. [reprint (PDF)]
 
1.  Angled cavity broad area quantum cascade lasers
Y. Bai, S. Slivken, Q.Y. Lu, N. Bandyopadhyay, and M. Razeghi
Applied Physics Letters, Vol. 100, Np. 8, p. 081106-1-- August 20, 2012 ...[Visit Journal]
Angled cavity broad area quantum cascade lasers (QCLs) are investigated with surface gratingbased distributed feedback (DFB) mechanisms. It is found that an angled cavity incorporating a one dimensional DFB with grating lines parallel to the laser facet offers the simplest solution for single mode and diffraction limited emission in the facet normal direction. A room temperature single mode QCL with the highest output power for wavelengths longer than 10 micron is demonstrated. This structure could be applied to a wide range of laser structures for power scaling along with spectral and spatial beam control. [reprint (PDF)]
 
1.  High operating temperature MWIR photon detectors based on Type II InAs/GaSb superlattice
M. Razeghi, S. Abdollahi Pour, E.K. Huang, G. Chen, A. Haddadi and B.M. Nguyen
SPIE Proceedings, Infrared Technology and Applications XXXVII, Orlando, FL, Vol. 8012, p. 80122Q-1-- April 26, 2011 ...[Visit Journal]
Recent efforts have been paid to elevate the operating temperature of Type II superlattice Mid Infrared photon detectors. Using M-structure superlattice, novel device architectures have been developed, resulting in significant improvement of the device performances. In this paper, we will compare different photodetector architectures and discuss the optimization scheme which leads to almost one order of magnitude of improvement to the electrical performance. At 150K, single element detectors exhibit a quantum efficiency above 50%, and a specific detectivity of 1.05x10(12) cm.Hz(1/2)/W. BLIP operation with a 300K background and 2π FOV can be reached with an operating temperature up to 180K. High quality focal plane arrays were demonstrated with a noise equivalent temperature difference (NEDT) of 11mK up to 120K. Human body imaging is achieved at 150K with NEDT of 150mK. [reprint (PDF)]
 

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