Center for Quantum Devices - Journal Articles and Conference Proceedings

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476.	High Quantum Efficiency AlGaN Solar-Blind Photodetectors R. McClintock, A. Yasan, K. Mayes, D. Shiell, S.R. Darvish, P. Kung and M. Razeghi Applied Physics Letters, 84 (8)-- February 23, 2004 We report AlGaN-based back-illuminated solar-blind ultraviolet p-i-n photodetectors with a peak responsivity of 136 mA/W at 282 nm without bias. This corresponds to a high external quantum efficiency of 60%, which improves to a value as high as 72% under 5 V reverse bias. We attribute the high performance of these devices to the use of a very-high quality AlN and Al_0.87Ga_0.13N/AlN superlattice material and a highly conductive Si–In co-doped Al_0.5Ga_0.5N layer reprint
477.	High Power 280 nm AlGaN Light Emitting Diodes Based on an Asymmetric Single Quantum Well K. Mayes, A. Yasan, R. McClintock, D. Shiell, S.R. Darvish, P. Kung, and M. Razeghi Applied Physics Letters, 84 (7)-- February 16, 2004 We demonstrate high-power AlGaN-based ultraviolet light-emitting diodes grown on sapphire with an emission wavelength of 280 nm using an asymmetric single-quantum-well active layer configuration on top of a high-quality AlGaN/AlN template layer. An output power of 1.8 mW at a pulsed current of 400 mA was achieved for a single 300 µm×300 µm diode. This device reached a high peak external quantum efficiency of 0.24% at 40 mA. An array of four diodes produced 6.5 mW at 880 mA of pulsed current. reprint
478.	Modeling of Type-II InAs/GaSb Superlattices Using Empirical Tight-Binding Method and Interface Engineering Y. Wei and M. Razeghi Physical Review B, 69 (8)-- February 15, 2004 We report the most recent work on the modeling of type-II InAs/GaSb superlattices using the empirical tight binding method in an sp3s* basis. After taking into account the antimony segregation in the InAs layers, the modeling accuracy of the band gap has been improved. Our calculations agree with our experimental results within a certain growth uncertainty. In addition, we introduce the concept of Ga_xIn_1-x type interface engineering in order to reduce the lattice mismatch between the superlattice and the GaSb (001) substrate to improve the overall superlattice material quality. reprint
479.	Passivation of Type-II InAs/GaSb Superlattice Photodiodes A. Gin, Y. Wei, J. Bae, A. Hood, J. Nah, and M. Razeghi International Conference on Metallurgical Coatings and Thin Films (ICMCTF), San Diego, CA; Thin Solid Films 447-448-- January 30, 2004 Recently, excellent infrared detectors have been demonstrated using Type-II InAs/GaSb superlattice materials sensitive at wavelengths from 3 μm to greater than 32 μm. These results indicate that Type-II superlattice devices may challenge the preponderance of HgCdTe and other state-of-the-art infrared material systems. As such, surface passivation is becoming an increasingly important issue as progress is made towards the commercialization of Type-II devices and focal plane array applications. This work focuses on initial attempts at surface passivation of Type-II InAs/GaSb superlattice photodiodes using PECVD-grown thin layers of SiO₂. Our results indicate that silicon dioxide coatings deposited at various temperatures improve photodetector resistivity by several times. Furthermore, reverse-bias dark current has been reduced significantly in passivated devices. reprint
480.	High Quantum Efficiency Solar-Blind Photodetectors R. McClintock, A. Yasan, K. Mayes, D. Shiell, S. Darvish, P. Kung and M. Razeghi SPIE Conference, Jose, CA, Vol. 5359, pp. 434-- January 25, 2004 We report AlGaN-based back-illuminated solar-blind p-i-n photodetectors with a record peak responsivity of 150 mA/W at 280 nm, corresponding to a high external quantum efficiency of 68%, increasing to 74% under 5 volts reverse bias. Through optimization of the p-AlGaN layer, we were able to remove the out-of-band negative photoresponse originating from the Schottky-like p-type metal contact, and hence significantly improve the degree of solar-blindness reprint
481.	Growth of Deep UV Light Emitting Diodes by Metalorganic Chemical Vapor Deposition A. Yasan, R. McClintock, K. Mayes, D. Shiell, S. Darvish, P. Kung and M. Razeghi SPIE Conference, Jose, CA, Vol. 5359, pp. 400-- January 25, 2004 We demonstrate high power AlGaN based ultraviolet light-emitting diodes (UV LEDs) with an emission wavelength of 280 nm using an asymmetric single quantum well active layer configuration on top of a high-quality AlGaN/AlN template layer grown by metalorganic chemical vapor deposition (MOCVD). An output power of 1.8 mW at a pulsed current of 400 mA was achieved for a single 300 µm × 300 µm diode. This device reached a high peak external quantum efficiency of 0.24% at 40 mA. An array of four diodes produced 6.5 mW at 880 mA of pulsed current. reprint
482.	Modeling Type-II InAs/GaSb Superlattices Using Empirical Tight-Binding Method: New Aspects Y. Wei, M. Razeghi, G.J. Brown, and M.Z. Tidrow SPIE Conference, Jose, CA, Vol. 5359, pp. 301-- January 25, 2004 The recent advances in the experimental work on the Type-II InAs/GaSb superlattices necessitate a modeling that can handle arbitrary layer thickness as well as different types of interfaces in order to guide the superlattice design. The empirical tight-binding method (ETBM) is a very good candidate since it builds up the Hamiltonian atom by atom. There has been a lot of research work on the modeling of Type-II InAs/GaSb superlattices using the ETBM. However, different groups generate very different accuracy comparing with experimental results. We have recently identified two major aspects in the modeling: the antimony segregation and the interface effects. These two aspects turned out to be of crucial importance governing the superlattice properties, especially the bandgap. We build the superlattice Hamiltonian using antimony segregated atomic profile taking into account the interface. Our calculations agree with our experimental results within growth uncertainties. In addition we introduced the concept of Ga_xIn_1-x type interface engineering, which will add another design freedom especially in the mid-wavelength infrared range (3~7 µm) in orderto reduce the lattice mismatch. reprint
483.	High Power, Room Temperature, Continuous-Wave Operation of Quantum Cascade Lasers Grown by GasMBE A. Evans, J. David, L. Doris, J.S. Yu, S. Slivken and M. Razeghi SPIE Conference, Jose, CA, Vol. 5359, pp. 188-- January 25, 2004 Very high power continuous-wave quantum cascade lasers are demonstrated in the mid-infrared (3 - 6 µm) wavelength range. λ~6 µm high-reflectivity coated QCLs are demonstrated producing over 370 mW continuous-wave power at room temperature with continuous-wave operation up to 333 K. Advanced heterostructure geometries, including the use of a thick electroplated gold, epilayer-side heat sink and a buried-ridge heterostructure are demonstrated to improve laser performance significantly when combined with narrow laser ridges. Recent significant improvements in CW operation are presented and include the development if narrow (9 µm-wide) ridges for high temperature CW operation. GasMBE growth of the strain-balanced λ~6 µm QCL heterostructure is discussed. X-ray diffraction measurements are presented and compared to computer simulations that indicate excellent layer and compositional uniformity of the structure. reprint
484.	High-temperature high-power continuous-wave operation of buried heterostructure quantum-cascade lasers A. Evans, J.S. Yu, J. David, L. Doris, K. Mi, S. Slivken, and M. Razeghi Applied Physics Letters, 84 (3)-- January 19, 2004 We report cw operation of buried heterostructure quantum-cascade lasers (λ=6 µm) using a thick electroplated Au top contact layer and epilayer-up bonding on a copper heat sink up to a temperature of 333 K (60 °C). The high cw optical output powers of 446 mW at 293 K, 372 mW at 298 K, and 30 mW at 333 K are achieved with threshold current densities of 2.19, 2.35, and 4.29 kA/cm² respectively, for a high-reflectivity-coated, 9-µm-wide and 3-mm-long laser reprint
485.	Cavity Length Effects of High-Temperature High-Power Continuous Wave Characteristics in Quantum-Cascade Lasers J.S. Yu, A. Evans, J. David, L. Doris, S. Slivken, and M. Razeghi Applied Physics Letters, 83 (25)-- December 22, 2003 We report the cavity-length dependent high-temperature high-power cw characteristics in λ=6 µm quantum-cascade lasers with a thick electroplated Au top contact layer. For a high-reflectivity (HR) coated 15 µm wide and 3 mm long laser, the cw operation is achieved up to 313 K (40 °C) with an output power of 17 mW. At 298 K, a very high cw output power of 213 mW is obtained for a HR coated 15 µm wide and 4 mm long laser. Thermal resistance is analyzed at temperatures above 283 K for HR coated lasers with different cavities. reprint
486.	4.5 mW Operation of AlGaN-based 267 nm Deep-Ultraviolet Light-Emitting Diodes A. Yasan, R. McClintock, K. Mayes, D. Shiell, L. Gautero, S.R. Darvish, P. Kung and M. Razeghi Applied Physics Letters, 83 (23)-- December 8, 2003 We demonstrate 4.5 mW output power from AlGaN-based single quantum well ultraviolet light-emitting diodes at a very short wavelength of 267 nm in pulsed operation mode. The output power in continuous-wave mode reaches a value of 165 µW at an injected current of 435 mA. The measurements were done on arrays of four devices flip chip bonded to AlN submounts for thermal management. reprint
487.	Photoluminescence Study of AlGaN-based 280 nm Ultraviolet Light-Emitting Diodes A. Yasan, R. McClintock, K. Mayes, D.H. Kim, P. Kung, and M. Razeghi Applied Physics Letters, 83 (20)-- November 17, 2003 We investigated optical properties of single quantum well AlGaN-based UV 280 nm light-emitting diodes using temperature-dependent photoluminescence (PL) measurement. We found an "S-shaped" temperature dependence of the peak energy. From the Arrhenius plot of integrated PL intensity, we speculate that dislocations as well as thermal emission of carriers out of the quantum well are responsible for the PL quenching behavior. Also a second nonradiative channel with much lower activation energy was found, the origin of which we believe to be quenching of the bound excitons reprint
488.	High Quality Type-II InAs/GaSb Superlattices with Cutoff Wavelength ~3.7 µm Using Interface Engineering Y. Wei, J. Bae, A. Gin, A. Hood, M. Razeghi, G.J. Brown, and M. Tidrow Journal of Applied Physics, 94 (7)-- October 1, 2003 We report the most recent advance in the area of Type-II InAs/GaSb superlattices that have cutoff wavelength of ~3.7 µm. With Ga_xIn_1–x type interface engineering techniques, the mismatch between the superlattices and the GaSb (001) substrate has been reduced to <0.1%. There is no evidence of dislocations using the best examination tools of x-ray, atomic force microscopy, and transmission electron microscopy. The full width half maximum of the photoluminescence peak at 11 K was ~4.5 meV using an Ar+ ion laser (514 nm) at fluent power of 140 mW. The integrated photoluminescence intensity was linearly dependent on the fluent laser power from 2.2 to 140 mW at 11 K. The temperature-dependent photoluminescence measurement revealed a characteristic temperature of one T1 = 245 K at sample temperatures below 160 K with fluent power of 70 mW, and T1 = 203 K for sample temperatures above 180 K with fluent power of 70 and 420 mW. reprint
489.	High-Power Continuous-Wave Operation of a 6 µm Quantum-Cascade Laser at Room Temperature J.S. Yu, S. Slivken, A. Evans, L. Doris, and M. Razeghi Applied Physics Letters, 83 (13)-- September 29, 2003 We report continuous-wave (cw) operation of quantum-cascade lasers (λ= 6 µm) using a thick electroplated Au top contact layer and epilayer-up bonding on a copper heat sink up to a temperature of 308 K (35 °C). The high cw optical output powers of 132 mW at 293 K and 21 mW at 308 K are achieved with threshold current densities of 2.29 and 2.91 kA/cm², respectively, for a high-reflectivity-coated 15 µm wide and 2 mm long laser. reprint
490.	Overview of Antimonide Based III-V Semiconductor Epitaxial Layers and their Applications at the Center for Quantum Devices M. Razeghi The European Physical Journal-Applied Physics, Vol. 23-- September 15, 2003 The properties of Sb-based III-V semiconductor compounds for optoelectronic applications in the mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) range were reviewed. The growths of the Sb-based binary, ternary and quaternary were studied by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). The structural, optical and electrical characterizations were carried out. Focal plane array, photoconductors and photodiodes were fabricated for the MWIR and LWIR range. Doublehetero structure (DH), multi-quantum well (MQW) and strained superlattice (SSL) lasers in the 3-5 μm range were fabricated. InAs-GaSb type-II superlattices were designed, grown and fabricated into photodetectors for the MWIR and LWIR range.
491.	Demonstration of 256x256 Focal Plane Arrays Based on Al-free GaInAs/InP QWIP J. Jiang, K. Mi, R. McClintock, M. Razeghi, G.J. Brown, and C. Jelen IEEE Photonics Technology Letters 15 (9)-- September 1, 2003 We report the first demonstration of an infrared focal plane array based on aluminum-free GaInAs-InP quantum-well infrared photodetectors (QWIPs).A unique positive lithography method was developed to perform indium-bump liftoff. The noise equivalent differential temperature (NEΔT) of 29 mK was achieved at 70 K with f/2 optics. reprint
492.	Very High Average Power at Room Temperature from λ ~ 5.9 μm Quantum Cascade Lasers J.S. Yu, S. Slivken, A. Evans, J. David and M. Razeghi Virtual Journal of Nanoscale Science & Technology 26-- May 26, 2003reprint
493.	Very High Average Power at Room Temperature from λ ~ 5.9 μm Quantum Cascade Lasers J.S. Yu, S. Slivken, A. Evans, J. David and M. Razeghi Applied Physics Letters, 82 (20)-- May 19, 2003 We report a very high average output power at room temperature for quantum-cascade lasers emitting at λ ~ 5.9 µm. For high-reflectivity-coated 2-mm-long cavities, a low threshold current density of 1.7 kA/cm² was obtained at room temperature. From 300 to 400 K, the characteristic temperature (T0) was 198 K. A maximum average output power of 0.67 W was achieved. In addition, 0.56 W average output power was observed at a duty cycle of 56%. reprint
494.	Quantum Sensing Using Type-II InAs/GaSb Superlattice for Infrared Detection M. Razeghi, A. Gin, Y. Wei, J. Bae, and J. Nah Microelectronics Journal, 34 (5-8)-- May 1, 2003 Large, regular arrays of bulk GaSb and InAs/GaSb Type-II superlattice pillars have been fabricated by electron beam lithography and dry etching. A 2.5 keV electron beam lithography system and metal evaporation are used to form the Au mask on superlattice and bulk substrates. Dry etching of these materials has been developed with BCl3:Ar, CH4:H2:Ar and cyclic CH₄:H₂:Ar/O₂ plasmas. Etch temperatures were varied from 20 to 150 °C. The diameter of the superlattice pillars was below 50 nm with regular 200 nm spacing. Bulk GaSb pillars were etched with diameters below 20 nm. Areas of dense nanopillars as large as 500 μm×500 μm were fabricated. The best height/diameter aspect ratio was approximately 10:1. To date, these are the smallest diameter III–V superlattice pillar structures reported, and the first nanopillars in the InAs/GaSb material system. The basic theory of these devices and surface passivation with SiO₂ and Si₃N₄ thin films has also been discussed. reprint
495.	High Performance Quantum Cascade Lasers at λ ~ 6 μm M. Razeghi, S. Slivken, J. Yu, A. Evans, and J. David Microelectronics Journal, 34 (5-8)-- May 1, 2003 This talk will focus on the recent efforts at the Center for Quantum Devices to deliver a high average power quantum cascade laser source at λ ~6 μm. Strain-balancing is used to reduce leakage for these shorter wavelength quantum cascade lasers. Further, the effect of reducing the doping in the injector is explored relative to the threshold current density and maximum average output power. Lastly, to demonstrate more of the potential of these devices, epilayer down bonding is explored as a technique to significantly enhance device performance. reprint
496.	High Power 3-12 μm Infrared Lasers: Recent Improvements and Future Trends M. Razeghi, S. Slivken, A. Tahraoui, A. Matlis, and Y.S. Park Advanced Research Workshop on Semiconductor Nanostructures, Queenstown, New Zealand; Proceedings -- February 5, 2003 In this paper, we discuss the progress of quantum cascade lasers (QCLs) grown by gas-source molecular beam epitaxy. Room temperature QCL operation has been reported for lasers emitting between 5-11 μm, with 9-11 μm lasers operating up to 425 K. Laser technology for the 3-5 μm range takes advantage of a strain-balanced active layer design. We also demonstrate record room temperature peak output powers at 9 and 11 μm (2.5 and 1 W, respectively) as well as record low 80K threshold current densities (250 A/cm²) for some laser designs. Preliminary distributed feedback (DFB) results are also presented and exhibit single mode operation for 9 μm lasers at room temperature. reprint
497.	High Power Quantum Cascade Lasers Operating at Room Temperature M. Razeghi and S. Slivken Journal of the Korean Physical Society, Vol. 42, pp. S637-S641-- February 1, 2003 In this paper, some key design and technology issues for development of high power quantum cascade lasers are discussed. The scaling of power output with the number of emitting stages is shown. As part of this work, high power, 75-stage, λ = 9 μm lasers have been demonstrated with a peak power of 7 W at room temperature. This power is a direct result of high quality material growth and a low loss waveguide design. Similar results are demonstrated at a shorter wavelength (λ = 6.1 μm) utilizing a strain-balanced active region/injector design. For a 30-stage structure, 2 W peak power and 250 mW average power have been demonstrated at room temperature. Lastly, a timeline comparison of QCL laser performance is presented in terms of room temperature threshold current density and peak output power for various groups.
498.	Recent Advances in InAs/GaSb Superlattices for Very Long Wavelength Infrared Detection G.J. Brown, F. Szmulowicz, K. Mahalingam, S. Houston, Y. Wei, A. Gin and M. Razeghi SPIE Conference, San Jose, CA, Vol. 4999, pp. 457-- January 27, 2003 New infrared (IR) detector materials with high sensitivity, multi-spectral capability, improved uniformity and lower manufacturing costs are required for numerous long and very long wavelength infrared imaging applications. One materials system has shown great theoretical and, more recently, experimental promise for these applications: InAs/In_xGa_1-xSb type-II superlattices. In the past few years, excellent results have been obtained on photoconductive and photodiode samples designed for infrared detection beyond 15 microns. The infrared properties of various compositions and designs of these type-II superlattices have been studied. The infrared photoresponse spectra are combined with quantum mechanical modeling of predicted absorption spectra to provide insight into the underlying physics behind the quantum sensing in these materials. Results for superlattice photodiodes with cut-off wavelengths as long as 25 microns are presented. reprint
499.	Very High Average Power Quantum Cascade Lasers by GasMBE S. Slivken and M. Razeghi SPIE Conference, San Jose, CA, Vol. 4999, pp. 59-- January 27, 2003 Very high average power QCLs are demonstrated within the 5.8 - 9 µm wavelength range. At longer wavelengths, scaling of the power is demonstrated by increasing the number of emitting regions in the waveguide core. At λ = 9 µm, over 3.5 W of peak power per facet has been demonstrated at room temperature for a single 25 µm by 3 mm diode, with an average power of 150 mW at 6% duty cycle. At shorter wavelengths, highly strain-balanced heterostructures are used to create a high coduction band offset and minimize leakage current. At λ = 6 µm, utilizing a high reflective coating and epilayer-down mounting of the laser, we demonstrate 225 mW of average power from a single facet at room temperature. Increasing the conduction band offset further and optimizing the doping in the injector region has led to demonstration of > 250 mW average power (λ = 5.8 µm) at > 50% duty cycle for a 20 µm by 2 mm HR coated diode bonded epilayer-down to a copper heatsink. Also at room temperature, use of Au electroplating and wider ridges has allowed us to further demonstrate without epilayer-down bonding, 0.67 W average power at 17% duty cycle from a single 40 µm by 2 mm HR coated laser. reprint
500.	Very high quality p-type Al_xGa_1-xN/GaN superlattice A. Yasan and M. Razeghi special ISDRS issue of Solid State Electronics Journal, 47-- January 1, 2003 Very high quality p-type Al_xGa_1−xN/GaN superlattice has been achieved through optimization of Mg flow and period of superlattice. Theoretical model was used to optimize the structure of superlattice by choosing suitable Al compositions and superlattice periods. The experiments show that for x=0.26, the resistivity is as low as 0.19 Ω cm and hole concentration is as high as 4.2×10¹⁸ cm⁻³, the highest values ever reported for p-type AlGaN/GaN superlattices. Hall effect measurement and admittance spectroscopy on the samples confirm the high quality of the superlattices. The activation energy calculated for p-type GaN and p-type A_0.1Ga_0.9N/GaN superlattice is estimated to be not, vert, similar 125 and 3 meV respectively. reprint

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