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4.  Investigations on the substrate dependence of the properties in nominally-undoped β-Ga2O3 thin films grown by PLD
F. H. Teherani ; D. J. Rogers ; V. E. Sandana ; P. Bove ; C. Ton-That ; L. L. C. Lem ; E. Chikoidze ; M. Neumann-Spallart ; Y. Dumont ; T. Huynh ; M. R. Phillips ; P. Chapon ; R. McClintock ; M. Razeghi
Proc. SPIE 10105, Oxide-based Materials and Devices VIII, 101051R (March 23, 2017)-- March 23, 2017 ...[Visit Journal]
Nominally-undoped Ga2O3 layers were deposited on a-, c- and r-plane sapphire substrates using pulsed laser deposition. Conventional x-ray diffraction analysis for films grown on a- and c-plane sapphire showed the layers to be in the β-Ga2O3 phase with preferential orientation of the (-201) axis along the growth direction. Pole figures revealed the film grown on r-plane sapphire to also be in theβ-Ga2O3 phase but with epitaxial offsets of 29.5°, 38.5° and 64° from the growth direction for the (-201) axis. Optical transmission spectroscopy indicated that the bandgap was ~5.2eV, for all the layers and that the transparency was > 80% in the visible wavelength range. Four point collinear resistivity and Van der Pauw based Hall measurements revealed the β-Ga2O3 layer on r-plane sapphire to be 4 orders of magnitude more conducting than layers grown on a- and c-plane sapphire under similar conditions. The absolute values of conductivity, carrier mobility and carrier concentration for the β-Ga2O3 layer on r-sapphire (at 20Ω-1.cm-1, 6 cm2/Vs and 1.7 x 1019 cm-3, respectively) all exceeded values found in the literature for nominally-undoped β-Ga2O3 thin films by at least an order of magnitude. Gas discharge optical emission spectroscopy compositional depth profiling for common shallow donor impurities (Cl, F, Si and Sn) did not indicate any discernable increase in their concentrations compared to background levels in the sapphire substrate. It is proposed that the fundamentally anisotropic conductivity in β-Ga2O3 combined with the epitaxial offset of the (-201) axis observed for the layer grown on r-plane sapphire may explain the much larger carrier concentration, electrical conductivity and mobility compared with layers having the (-201) axis aligned along the growth direction. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. [reprint (PDF)]
 
4.  Quntum Cascade Laser Breakthrough for Advanced Remote Detection
Manijeh Razeghi, Wenjia Zhou, Donghai Wu, Ryan McClintock, and Steven Slivken, Northwestern University
www.photonics.com-- November 1, 2016
The atoms in a molecule can bend, stretch and rotate with respect to one an­other, and these excitations are largely optically active. Most molecules, from simple to moderately complex, have a characteristic absorption spectrum in the 3- to 14-µrn wavelength range that can be uniquely identified and quantified in real time. Infrared spectroscopy has been used to study these absorption features and de­velop different molecular "fingerprints."
 
4.  Advances in antimonide-based Type-II superlattices for infrared detection and imaging at center for quantum devices
M. Razeghi, A. Haddadi, A.M. Hoang, E.K. Huang, G. Chen, S. Bogdanov, S.R. Darvish, F. Callewaert, R. McClintock
Infrared Physics & Technology, Volume 59, Pages 41-52 (2013)-- July 1, 2013 ...[Visit Journal]
Type-II InAs/GaSb superlattices (T2SLs), a system of multi-interacting quantum wells, was introduced by Nobel Laureate L. Esaki in the 1970s. Since then, this material system has drawn a lot of attention especially for infrared detection. In recent years, T2SL material system has experienced incredible improvements in material quality, device structure designs and device fabrication process which elevated the performances of T2SL-based photo-detectors to a comparable level to the state-of-the-art material systems for infrared detection such as Mercury Cadmium Telluride (MCT). In this paper, we will present the current status of T2SL-based photo-detectors and focal plane arrays for imaging in different infrared regions, from SWIR to VLWIR, and the future outlook of this material system. [reprint (PDF)]
 
4.  Surface plasmon enhanced light emission from AlGaN-based ultraviolet light-emitting diodes grown on Si (111)
Chu-Young Cho, Yinjun Zhang, Erdem Cicek, Benjamin Rahnema, Yanbo Bai, Ryan McClintock, and Manijeh Razeghi
Appl. Phys. Lett. 102, 211110 (2013)-- May 31, 2013 ...[Visit Journal]
We report on the development of surface plasmon (SP) enhanced AlGaN-based multiple quantum wells (MQWs) ultraviolet (UV) light-emitting diodes (LEDs) grown on silicon (111) substrates. In order to generate SP-coupling with the radiating dipoles in MQWs, an aluminum layer is selectively deposited in holes etched in the top p-AlGaN to p-GaN layers. After flip-chip bonding and substrate removal, an optical output power of ∼1.2 mW is achieved at an emission wavelength of 346 nm; the output power of these UV LEDs with Al layer is increased by 45% compared to that of conventional UV LEDs without Al layer. This enhancement can be attributed to an increase in the spontaneous emission rate and improved internal quantum efficiency via resonance coupling between excitons in MQWs and SPs in the aluminum layer. [reprint (PDF)]
 
4.  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)]
 
4.  Near milliwatt power AlGaN-based ultraviolet light emitting diodes based on lateral epitaxial overgrowth of AlN on Si(111)
Y. Zhang, S. Gautier, C. Cho, E. Cicek, Z, Vashaei, R. McClintock, C. Bayram, Y. Bai and M. Razeghi
Applied Physics Letters, Vol. 102, No. 1, p. 011106-1-- January 7, 2013 ...[Visit Journal]
We report on the growth, fabrication, and device characterization of AlGaN-based thin-film ultraviolet (UV) (λ ∼ 359 nm) light emitting diodes (LEDs). First, AlN/Si(111) template is patterned. Then, a fully coalesced 7-μm-thick lateral epitaxial overgrowth (LEO) of AlN layer is realized on patterned AlN/Si(111) template followed by UV LED epi-regrowth. Metalorganic chemical vapor deposition is employed to optimize LEO AlN and UV LED epitaxy. Back-emission UV LEDs are fabricated and flip-chip bonded to AlN heat sinks followed by Si(111) substrate removal. A peak pulsed power and slope efficiency of ∼0.6 mW and ∼1.3 μW/mA are demonstrated from these thin-film UV LEDs, respectively. For comparison, top-emission UV LEDs are fabricated and back-emission LEDs are shown to extract 50% more light than top-emission ones. [reprint (PDF)]
 
4.  Monolithic terahertz source
Q. Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai and M. Razeghi
Nature Photonics | Research Highlights -- July 31, 2014 ...[Visit Journal]
To date, the production of continuous-wave terahertz (THz) sources based on intracavity difference-frequency generation from mid-infrared quantum cascade lasers operating at room temperature has proved elusive. A critical problem is that, to achieve a large nonlinear susceptibility for frequency conversion, the active region of the quantum cascade laser requires high doping, which elevates the lasing threshold current density. Now, Quan-Yong Lu and colleagues from Northwestern University in the USA have overcome this problem and demonstrated a room-temperature continuous-wave THz source based on difference-frequency generation in quantum cascade lasers. They designed quantum-well structures based on In0.53Ga0.47As/In0.52Al0.48As material system for two mid-infrared wavelengths. The average doping in the active region was about 2.5 × 1016 cm−3. A buried ridge, buried composite distributed-feedback waveguide with the Čerenkov phase-matching scheme was used to reduce the waveguide loss and enhance heat dissipation. As a result, single-mode emission at 3.6 THz was observed at 293 K. The continuous-wave THz power reached 3 μW with a conversion efficiency of 0.44 mW W−2 from mid-infrared to THz waves. Using a similar device design, a THz peak power of 1.4 mW was achieved in pulse mode. [reprint (PDF)]
 
4.  Continuous wave, room temperature operation of λ ~ 3μm quantum cascade laser
N. Bandyopadhyay, Y. Bai, S. Tsao, S. Nida, S. Slivken and M. Razeghi
SPIE Proceedings, Vol. 8631, p. 86310M-1, Photonics West, San Francisco, CA-- February 3, 2013 ...[Visit Journal]
Quantum Cascade Lasers (QCLs), operating in continuous wave (CW) at room temperature(RT) in 3-3.5 μm spectral range, which overlaps the spectral fingerprint region of many hydrocarbons, is essential in spectroscopic trace gas detection, environment monitoring, and pollution control. A 3 μm QCL, operating in CW at RT is demonstrated. This initial result makes it possible, for the most popular material system (AlInAs/GaInAs on InP) used in QCLs in mid-infrared and long-infrared, to cover the entire spectral range of mid-infrared atmospheric window (3-5 μm). In0.79Ga0.21As/In0.11Al0.89As strain balanced superlattice, which has a large conduction band offset, was grown. The strain was balanced with composite barriers (In0.11Al0.89As /In0.4Al0.6As) in the injector region, to eliminate the need of extremely high compressively strained GaInAs, whose pseudomorphic growth is very difficult. [reprint (PDF)]
 
4.  Highly selective two-color mid-wave and long-wave infrared detector hybrid based on Type-II superlattices
E.K. Huang, M.A. Hoang, G. Chen, S.R. Darvish, A. Haddadi, and M. Razeghi
Optics Letters, Vol. 37, No. 22, p. 4744-4746-- November 15, 2012 ...[Visit Journal]
We report a two-color mid-wave infrared (MWIR) and long-wave infrared (LWIR) co-located detector with 3 μm active region thickness per channel that is highly selective and can perform under high operating temperatures for the MWIR band. Under back-side illumination, a temperature evolution study of the MWIR detector’s electro-optical performance found the 300 K background-limit with 2π field-of-view to be achieved below operating temperatures of 160 K, at which the temperature’s 50% cutoff wavelength was 5.2 μm. The measured current reached the system limit of 0.1 pA at 110 K for 30 μm pixel-sized diodes. At 77 K, where the LWIR channel operated with a 50% cutoff wavelength at 11.2 μm, an LWIR selectivity of ∼17% was achieved in the MWIR wave band between 3 and 4.7 μm, making the detector highly selective. [reprint (PDF)]
 
4.  Growth of AlGaN on silicon substrates: a novel way to make back-illuminated ultraviolet photodetectors
Ryan McClintock ; Manijeh Razeghi
Proc. SPIE 9555, Optical Sensing, Imaging, and Photon Counting: Nanostructured Devices and Applications, 95550U-- August 28, 2015 ...[Visit Journal]
AlGaN, with its tunable wide-bandgap is a good choice for the realization of ultraviolet photodetectors. AlGaN films tend to be grown on foreign substrates such as sapphire, which is the most common choice for back-illuminated devices. However, even ultraviolet opaque substrates like silicon holds promise because, silicon can be removed by chemical treatment to allow back-illumination,1 and it is a very low-cost substrate which is available in large diameters up to 300 mm. However, Implementation of silicon as the solar-blind PD substrates requires overcoming the lattice-mismatch (17%) with the AlxGa1-xN that leads to high density of dislocation and crack-initiating stress. In this talk, we report the growth of thick crack-free AlGaN films on (111) silicon substrates through the use of a substrate patterning and mask-less selective area regrowth. This technique is critical as it decouples the epilayers and the substrate and allows for crack-free growth; however, the masking also helps to reduce the dislocation density by inclining the growth direction and encouraging dislocations to annihilate. A back-illuminated p-i-n PD structure is subsequently grown on this high quality template layer. After processing and hybridizing the device we use a chemical process to selectively remove the silicon substrate. This removal has minimal effect on the device, but it removes the UV-opaque silicon and allows back-illumination of the photodetector. We report our latest results of back-illuminated solar-blind photodetectors growth on silicon. [reprint (PDF)]
 
4.  InAs/InAs1-xSbx type-II superlattices for high performance long wavelength infrared detection
A. Haddadi , G. Chen , R. Chevallier , A. M. Hoang , and M. Razeghi
Appl. Phys. Lett. 105, 121104 (2014)-- September 22, 2014 ...[Visit Journal]
High performance long-wavelength infrared nBn photodetectors based on InAs/InAs1−xSbx type-II superlattices on GaSb substrate have been demonstrated. The photodetector's 50% cut-off wavelength was ∼10 μm at 77 K. 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 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 at 77 K, the photodetector exhibited a specific detectivity of 2.8 × 1011 cm·Hz1/2·W-1. [reprint (PDF)]
 
4.  High power, continuous wave, room temperature operation of λ ~ 3.4 μm and λ ~ 3.55 μm InP-based quantum cascade lasers
N. Bandyopadhyay, S. Slivken, Y. Bai and M. Razeghi
Applied Physics Letters, Vol. 100, No. 21, p. 212104-1-- May 21, 2012 ...[Visit Journal]
We report two highly strain-balanced InP-based AlInAs/GaInAs quantum cascade lasers emitting near 3.39 and 3.56 . A pulsed threshold current density of only 1.1 kA/cm² has been achieved at room temperature for both lasers with characteristic temperatures (T0) of 166  K and 152  K, respectively. The slope efficiency is also relatively temperature insensitive with characteristic temperatures (T1) of 116 K and 191  K, respectively. Continuous wave powers of 504 mW and 576 mW are obtained at room temperature, respectively. This was accomplished without buried ridge processing. [reprint (PDF)]
 
4.  High power broad area quantum cascade lasers
Y. Bai, S. Slivken, S.R. Darvish, A. Haddadi, B. Gokden and M. Razeghi
Applied Physics Letters, Vol. 95, No. 22, p. 221104-1-- November 30, 2009 ...[Visit Journal]
Broad area quantum cascade lasers (QCLs) are studied with ridge widths up to 400 µm, in room temperature pulsed mode operation at an emission wavelength around 4.45 µm. The peak output power scales linearly with the ridge width. A maximum total peak output power of 120 W is obtained from a single 400-µm-wide device with a cavity length of 3 mm. A stable far field emission characteristic is observed with dual lobes at ±38° for all tested devices, which suggests that these broad area QCLs are highly resistant to filamentation. [reprint (PDF)]
 
3.  High performance bias-selectable 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
SPIE Proceedings, Vol. 8631, p. 86311K-1, Photonics West, San Francisco, CA-- February 5, 2013 ...[Visit Journal]
Active and passive imaging in a single camera based on the combination of short-wavelength and mid-wavelength infrared detection is highly needed in a number of tracking and reconnaissance missions. Due to its versatility in band-gap engineering, Type-II InAs/GaSb/AlSb superlattice has emerged as a candidate highly suitable for this multi-spectral detection. In this paper, we report the demonstration of high performance bias-selectable dual-band short-/mid-wavelength infrared photodetectors based on InAs/GaSb/AlSb type-II superlattice with designed cut-off wavelengths of 2 μm and 4 μm. Taking advantages of the high performance short-wavelength and mid-wavelength single color photodetectors, back-to-back p-i-n-n-i-p photodiode structures were grown on GaSb substrate by molecular beam epitaxy. At 150 K, the short-wave channel exhibited a quantum efficiency of 55%, a dark current density of 1.0x10-9 A/cm² at -50 mV bias voltage, providing an associated shot noise detectivity of 3.0x1013 Jones. The mid-wavelength channel exhibited a quantum efficiency of 33% and a dark current density of 2.6x10-5 A/cm² at 300 mV bias voltage, resulting in a detectivity of 4.0x1011 Jones. The operations of the two absorber channels are selectable by changing the polarity of applied bias voltage. [reprint (PDF)]
 
3.  Optimizing facet coating of quantum cascade lasers for low power consumption
Y. Bai, S.R. Darvish, N. Bandyopadhyay, S. Slivken and M. Razeghi
Journal of Applied Physics, Vol. 109, No. 5, p. 053103-1-- March 1, 2011 ...[Visit Journal]
Typical high power consumption (∼10 W) of mid-infrared quantum cascade lasers (QCLs) has been a serious limitation for applications in battery powered systems. A partial high-reflection (PHR) coating technique is introduced for power downscaling with shorter cavity lengths. The PHR coating consists of a double layer dielectric of SiO2 and Ge. With this technique, a 4.6 μm QCL with an ultra low threshold power consumption of less than a watt (0.83 W) is demonstrated in room temperature continuous wave operation. At 25°C, the maximum output power and wall plug efficiency are 192 mW and 8.6%, respectively. [reprint (PDF)]
 
3.  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)]
 
3.  Engineering future light emitting diodes and photovoltaics with inexpensive materials: Integrating ZnO and Si into GaN-based devices
C. Bayram ; K. T. Shiu ; Y. Zhu ; C. W. Cheng ; D. K. Sadana ; F. H. Teherani ; D. J. Rogers ; V. E. Sandana ; P. Bove ; Y. Zhang ; S. Gautier ; C.-Y. Cho ; E. Cicek ; Z. Vashaei ; R. McClintock ; M. Razeghi
Proc. SPIE 8626, Oxide-based Materials and Devices IV, 86260L (March 18, 2013)-- March 18, 2013 ...[Visit Journal]
Indium Gallium Nitride (InGaN) based PV have the best fit to the solar spectrum of any alloy system and emerging LED lighting based on InGaN technology and has the potential to reduce energy consumption by nearly one half while enabling significant carbon emission reduction. However, getting the maximum benefit from GaN diode -based PV and LEDs will require wide-scale adoption. A key bottleneck for this is the device cost, which is currently dominated by the substrate (i.e. sapphire) and the epitaxy (i.e. GaN). This work investigates two schemes for reducing such costs. First, we investigated the integration of Zinc Oxide (ZnO) in InGaN-based diodes. (Successful growth of GaN on ZnO template layers (on sapphire) was illustrated. These templates can then be used as sacrificial release layers for chemical lift-off. Such an approach provides an alternative to laser lift-off for the transfer of GaN to substrates with a superior cost-performance profile, plus an added advantage of reclaiming the expensive single-crystal sapphire. It was also illustrated that substitution of low temperature n-type ZnO for n-GaN layers can combat indium leakage from InGaN quantum well active layers in inverted p-n junction structures. The ZnO overlayers can also double as transparent contacts with a nanostructured surface which enhances light in/out coupling. Thus ZnO was confirmed to be an effective GaN substitute which offers added flexibility in device design and can be used in order to simultaneously reduce the epitaxial cost and boost the device performance. Second, we investigated the use of GaN templates on patterned Silicon (100) substrates for reduced substrate cost LED applications. Controlled local metal organic chemical vapor deposition epitaxy of cubic phase GaN with on-axis Si(100) substrates was illustrated. Scanning electron microscopy and transmission electron microscopy techniques were used to investigate uniformity and examine the defect structure in the GaN. Our results suggest that groove structures are very promising for controlled local epitaxy of cubic phase GaN. Overall, it is concluded that there are significant opportunities for cost reduction in novel hybrid diodes based on ZnO-InGaN-Si hybridization. [reprint (PDF)]
 
3.  Core-shell GaN-ZnO Moth-eye Nanostructure Arrays Grown on a-SiO2/Si (111) as a basis for Improved InGaN-based Photovoltaics and LEDs
D.J. Rogers, V.E. Sandana, S. Gautier, T. Moudakir, M. Abid, A. Ougazzaden, F. Hosseini Teherani, P. Bove, M. Molinari, M. Troyon, M. Peres, Manuel J. Soares, A.J. Neves, T. Monteiro, D. McGrouther, J.N. Chapman, H.-J. Drouhin, R. McClintock, M. Razeghi
Photonics and Nanostructures - Fundamentals and Applications (2015)-- March 30, 2015 ...[Visit Journal]
Self-forming, vertically-aligned, ZnO moth-eye-like nanoarrays were grown by catalyst-free pulsed laser deposition on a-SiO2/Si (111) substrates. X-Ray Diffraction (XRD) and Cathodoluminescence (CL) studies indicated that nanostructures were highly c-axis oriented wurtzite ZnO with strong near band edge emission. The nanostructures were used as templates for the growth of non-polar GaN by metal organic vapor phase epitaxy. XRD, scanning electron microscopy, energy dispersive X-ray microanalysis and CL revealed ZnO encapsulated with GaN, without evidence of ZnO back-etching. XRD showed compressive epitaxial strain in the GaN, which is conducive to stabilization of the higher indium contents required for more efficient green light emitting diode (LED) and photovoltaic (PV) operation. Angular-dependent specular reflection measurements showed a relative reflectance of less than 1% over the wavelength range of 400–720 nm at all angles up to 60°. The superior black-body performance of this moth-eye-like structure would boost LED light extraction and PV anti-reflection performance compared with existing planar or nanowire LED and PV morphologies. The enhancement in core conductivity, provided by the ZnO, would also improve current distribution and increase the effective junction area compared with nanowire devices based solely on GaN. [reprint (PDF)]
 
3.  Near bulk-limited R0A of long-wavelength infrared type-II InAs/GaSb superlattice photodiodes with polyimide surface passivation
Andrew Hood, Pierre-Yves Delaunay, Darin Hoffman, Binh-Minh Nguyen, Yajun Wei, Manijeh Razeghi, and Vaidya Nathan
Applied Physics Letters 90, 233513-- June 4, 2007 ...[Visit Journal]
Effective surface passivation of Type-II InAs/GaSb superlattice photodiodes with cutoff wavelengths in the long-wavelength infrared is presented. A stable passivation layer, the electrical properties of which do not change as a function of the ambient environment nor time, has been prepared by a solvent-based surface preparation, vacuum desorption, and the application of an insulating polyimide layer. Passivated photodiodes, with dimensions ranging from 400×400 to 25×25 µm2, with a cutoff wavelength of ~11 µm, exhibited near bulk-limited R0A values of ~12 Ω·cm2, surface resistivities in excess of 104 Ω·cm, and very uniform current-voltage behavior at 77 K. [reprint (PDF)]
 
3.  Overview of Quantum Cascade Laser Research at the Center for Quantum Devices
S. Slivken, A. Evans, J. Nguyen, Y. Bai, P. Sung, S.R. Darvish, W. Zhang and M. Razeghi
SPIE Conference, January 20-25, 2008, San Jose, CA Proceedings – Quantum Sensing and Nanophotonic Devices V, Vol. 6900, p. 69000B-1-8.-- February 1, 2008 ...[Visit Journal]
Over the past several years, our group has endeavored to develop high power quantum cascade lasers for a variety of remote and high sensitivity infrared applications. The systematic optimization of laser performance has allowed for demonstration of high power, continuous-wave quantum cascade lasers operating above room temperature. In the past year alone, the efficiency and power of our short wavelength lasers (~4.8 µm) has doubled. In continuous wave at room temperature, we have now separately demonstrated ~10% wallplug efficiency and ~700 mW of output power. Up to now, we have been able to show that room temperature continuous wave operation with > 100 mW output power in the 3.8 < λ < 11.5 µm wavelength range is possible. [reprint (PDF)]
 
3.  Hole-initiated multiplication in back-illuminated GaN avalanche photodiodes
R. McClintock, J.L. Pau, K. Minder, C. Bayram, P. Kung and M. Razeghi
Applied Physics Letters, Vol. 90 No. 14, p. 141112-1-- April 2, 2007 ...[Visit Journal]
Avalanche p-i-n photodiodes were fabricated on AlN templates for back illumination. Structures with different intrinsic layer thicknesses were tested. A critical electric field of 2.73 MV/cm was estimated from the variation of the breakdown voltage with thickness. From the device response under back and front illumination and the consequent selective injection of holes and electrons in the junction, ionization coefficients were obtained for GaN. The hole ionization coefficient was found to be higher than the electron ionization coefficient as predicted by theory. Excess multiplication noise factors were also calculated for back and front illumination, and indicated a higher noise contribution for electron injection. [reprint (PDF)]
 
3.  Investigation of impurities in type-II InAs/GaSb superlattices via capacitance-voltage measurement
G. Chen, A. M. Hoang, S. Bogdanov, A. Haddadi, P. R. Bijjam, B.-M. Nguyen, and M. Razeghi
Applied Physics Letters 103, 033512 (2013)-- July 17, 2013 ...[Visit Journal]
Capacitance-voltage measurement was utilized to characterize impurities in the non-intentionally doped region of Type-II InAs/GaSb superlattice p-i-n photodiodes. Ionized carrier concentration versus temperature dependence revealed the presence of a kind of defects with activation energy below 6 meV and a total concentration of low 1015 cm−3. Correlation between defect characteristics and superlattice designs was studied. The defects exhibited a p-type behavior with decreasing activation energy as the InAs thickness increased from 7 to 11 monolayers, while maintaining the GaSb thickness of 7 monolayers. With 13 monolayers of InAs, the superlattice became n-type and the activation energy deviated from the p-type trend. [reprint (PDF)]
 
3.  Background limited long wavelength infrared type-II InAs/GaSb superlattice photodiodes operating at 110 K
B.M. Nguyen, D. Hoffman, E.K. Huang, P.Y. Delaunay, and M. Razeghi
Applied Physics Letters, Vol. 93, No. 12, p. 123502-1-- September 22, 2008 ...[Visit Journal]
The utilization of the P+-pi-M-N+ photodiode architecture in conjunction with a thick active region can significantly improve long wavelength infrared Type-II InAs/GaSb superlattice photodiodes. By studying the effect of the depletion region placement on the quantum efficiency in a thick structure, we achieved a topside illuminated quantum efficiency of 50% for an N-on-P diode at 8.0 µm at 77 K. Both the double heterostructure design and the application of polyimide passivation greatly reduce the surface leakage, giving an R0A of 416 Ω·cm2 for a 1% cutoff wavelength of 10.52 µm, a Shot–Johnson detectivity of 8.1×1011 cm·Hz½/W at 77 K, and a background limited operating temperature of 110 K with 300 K background. [reprint (PDF)]
 
3.  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)]
 
3.  Long-Wavelength InAsSb Photoconductors Operated at Near Room Temperatures (200-300 K)
J.D. Kim, D. Wu, J. Wojkowski, J. Piotrowski, J. Xu, and M. Razeghi
Applied Physics Letters., 68 (1),-- January 1, 1996 ...[Visit Journal]
Long-wavelength InAs1−xSbx photoconductors operated without cryogenic cooling are reported. The devices are based on p-InAs1−xSbx/p-InSb heterostructures grown on (100) semi-insulating GaAs substrates by low pressure metalorganic chemical vapor deposition (LP‐MOCVD). Photoreponse up to 14 μm has been obtained in a sample with x=0.77 at 300 K, which is in good agreement with the measured infrared absorption spectra. The corresponding effective lifetime of ≊0.14 ns at 300 K has been derived from stationary photoconductivity. The Johnson noise limited detectivity at λ=10.6 μm is estimated to be about 3.27×107 cm· Hz½/W at 300 K. [reprint (PDF)]
 

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