Center for Quantum Devices - Journal Articles and Conference Proceedings

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501.	Artificial Atoms: Solution for Infrared Multicolor Focal Plane Arrays M. Razeghi Proceedings of the American Physical Society, Annual APS March Meeting-- January 1, 2003 Using bandgap engineering, we have developed a new type-II superlattice detector design based on InAs/GaSb superlattices with suppressed Auger processes. The experimental results show nearly one order of magnitude lower Auger recombination rate at room temperature in these detectors compared to typical intrinsic (HgCdTe) detectors with similar bandgap. Photoconductors based on this design show a detectivity of 1.3x10⁸ cm·Hz^½/W at 11 μm at room temperature, while photodiodes show a zero-bias detectivity of 1.2x10⁸ cm·Hz^½/W at 8 micron at room temperature. These values are comparable to the detectivity of microbolometers. However, the measured response time of the detector is less than 60 nsec which is more than five orders of magnitude faster than microbolometers. Similarly, we have implemented empirical tight binding method to design VLWIR detectors. We have obtained excellent results for devices with cutoff wavelengths up to 25 micron, for the first time. Excellent agreement between theory and experimental results have been reached for these devices. A peak detectivity of 5x10¹⁰ cm·Hz^½/W has been obtained for 19 micron photodetectors at 80 K. We propose the possibility of a new technique for the lateral confinement of electrons in type-II superlattices. We have achieved very uniform arrays of 100 nm diameter pillars using electron beam lithography followed by dry etching. By putting the gate voltage on the side of the pillars, the allowed electronic energy states can be changed and hence the cut-off wavelength. A tunable infrared detector operating in the mid and long wavelength infrared range based on these gated pillars can therefore be conceived. This talk will cover the recent advances in type-II superlattices for optoelectronic devices and how nanotechnology and artificial atoms can improve their performances and provide multicolor focal plane arrays.
502.	High Performance Quantum Cascade Laser Results at the Centre for Quantum Devices M. Razeghi and S. Slivken Physica Status Solidi, 195 (1)-- January 1, 2003 In this paper, we review some of the history and recent results related to the development of the quantum cascade laser at the Center for Quantum Devices. The fabrication of the quantum cascade laser is described relative to growth, characterization, and processing. State-of-the-art testing results for 5-11 μm lasers will be then be explored, followed by a future outlook for the technology. reprint
503.	High Power Quantum Cascade Lasers (QCLs) Grown by GasMBE M. Razeghi and S. Slivken Opto-Electronics Review, 11 (2)-- January 1, 2003 This paper is a brief summary of the technological development and state-of-the-art performance of quantum cascade lasers (QCLs) produced at the Centre for Quantum Devices. Laser design will be discussed, as well as experimental details of device fabrication. Recent work has focused on the development of high peak and average power QCLs emitting at room temperature and above. Scaling of the output is demonstrated by increasing the number of emitting regions in the waveguide core. At λ = 9 µm, over 7 W of peak power has bee demonstrated at room temperature for a single diode, with an average power of 300 mW at 6% duty cycle. At shorter wavelengths, laser development includes the use of highly strain-balanced heterostructures in order to maintain a high conduction band offset and minimize leakage current. At λ = 6 µm, utilizing a high reflective coating and epilayer-down mounting of the laser, we have demonstrated 225 mW of average power from a single facet at room temperature. Lastly, these results are put in the perspective of other reported results and possible future directions are discussed.
504.	High-Average-Power, High-Duty-Cycle (~6 μm) Quantum Cascade Lasers S. Slivken, A. Evans, J. David, and M. Razeghi Virtual Journal of Nanoscience & Technology 9-- December 9, 2002reprint
505.	High-Average-Power, High-Duty-Cycle (~6 μm) Quantum Cascade Lasers S. Slivken, A. Evans, J. David, and M. Razeghi Applied Physics Letters, 81 (23)-- December 2, 2002 High-power quantum cascade lasers emitting at λ = 6.1 μm are demonstrated. Accurate control of growth parameters and strain balancing results in a near-perfect lattice match, which leads to excellent material quality. Excellent peak power for uncoated lasers, up to 1.5 W per facet for a 21 μm emitter width, is obtained at 300 K for 30 period structures. The threshold current density at 300 K is only 2.4 kA/cm². From 300 to 425 K, the laser exhibits a characteristic temperature T₀ of 167 K. Next, Y₂O₃/Ti/Au mirror coatings were deposited on 1.5 mm cavities and mounted epilayer down. These lasers show an average output power of up to 225 mW at 17% duty cycle, and still show 8 mW average power at 45% duty cycle. reprint
506.	Type-II InAs/GaSb superlattice photovoltaic detectors with cutoff wavelength approaching 32 μm Y. Wei, A. Gin, M. Razeghi and G.J. Brown Applied Physics Letters, 81 (19)-- November 4, 2002 We report the most recent advance in the area of type-II InAs/GaSb superlattice photovoltaic detectors that have cutoff wavelengths beyond 25 μm, with some at nearly 32 μm. The photodiodes with a heterosuperlattice junction showed Johnson noise limited peak detectivity of 1.05 x 10¹⁰ cm Hz^½/W at 15 μm under zero bias, and peak responsivity of 3 A/W under -40 mV reverse bias at 34 K illuminated by ~300 K background with a 2π field-of-view. The maximum operating temperature of these detectors ranges from 50 to 65 K. No detectable change in the blackbody response has been observed after 5-6 thermal cyclings, with temperature varying between 15 and 296 K in vacuum. reprint
507.	High Power Quantum Cascade Lasers (QCLs) Grown by GasMBE M. Razeghi and S. Slivken SPIE Proceedings, International Conference on Solid State Crystals (ICSSC), Zakopane, Poland, -- October 14, 2002 This paper is a brief summary of the technological development and state-of-the-art performance of quantum cascade lasers produced at the Centre for Quantum Devices. Laser design will be discussed, as well as experimental details of device fabrication. Recent work has focused on the development of high peak and average power QCLs emitting at room temperature and above. Scaling of the output is demonstrated by increasing the number of emitting regions in the waveguide core. At λ = 9 µm, over 7 W of peak power has been demonstrated at room temperature for a single diode, with an average power of 300 mW at 6% duty cycle. At shorter wavelengths, laser development includes the use of highly strain-balanced heterostructures in order to maintain a high conduction band offset and minimize leakage current. At λ = 6 µm, utilizing a high reflective coating and epilayer-down mounting of the laser, we have demonstrated 225 mW of average power from a single facet at room temperature. Lastly, these results are put in perspective of other reported results and possible future directions are discussed. reprint
508.	Comparison of ultraviolet light-emitting diodes with peak emission at 340 nm grown on GaN substrate and sapphire A. Yasan, R. McClintock, K. Mayes, S.R. Darvish, H. Zhang, P. Kung, M. Razeghi, S.K. Lee and J.Y. Han Applied Physics Letters, 81 (12)-- September 16, 2002 Based on AlInGaN/AlInGaN multiquantum wells, we compare properties of ultraviolet light-emitting diodes (LED) with peak emission at 340 nm grown on free-standing hydride vapor phase epitaxially grown GaN substrate and on sapphire. For the LED grown on GaN substrate, a differential resistance as low as 13 Ω and an output power of more than one order of magnitude higher than that of the same structure grown on sapphire are achieved. Due to higher thermal conductivity of GaN, output power of the LEDs saturates at higher injection currents compared to the devices grown on sapphire. reprint
509.	Top-emission ultraviolet light-emitting diodes with peak emission at 280 nm A. Yasan, R. McClintock, K. Mayes, S.R. Darvish, P. Kung, and M. Razeghi Virtual Journal of Nanoscale Science & Technology, 5-- August 5, 2002reprint
510.	Top-emission ultraviolet light-emitting diodes with peak emission at 280 nm A. Yasan, R. McClintock, K. Mayes, S.R. Darvish, P. Kung, and M. Razeghi Applied Physics Letters 81 (5)-- July 29, 2002 We demonstrate light emission at 280 nm from UV light-emitting diodes consisting of AlInGaN/AlInGaN multiple quantum wells. Turn-on voltage of the devices is ~5 V with a differential resistance of ~40 Ω. The peak emission wavelength redshifts ~1 nm at high injection currents. reprint
511.	Optoelectronic Integrated Circuits (OEICs) for Next Generation WDM Communications M. Razeghi and S. Slivken SPIE Conference, Boston, MA, -- July 29, 2002 This paper reviews some of the key enabling technologies for present and future optoelectronic intergrated circuits. This review concentrates mainly on technology for lasers, waveguides, modulators, and fast photodetectors as the basis for next generation communicatiosn systems. Emphasis is placed on intergrations of components and mass production of a generic intelligent tranciever. reprint
512.	High-Power (~9 μm) Quantum Cascade Lasers S. Slivken, Z. Huang, A. Evans, and M. Razeghi Applied Physics Letters 80 (22)-- June 3, 2002 High-power quantum cascade lasers emitting at λ > 9 μm are demonstrated. Accurate control of layer thickness and interfaces is evidenced by x-ray diffraction. Excellent peak power for uncoated lasers, up to 3.5 W per facet for a 25 μm emitter width, is obtained at 300 K for 75 period structures. The threshold current density at 300 K is only 1.4 kA/cm². From 300 to 425 K, the laser exhibits a characteristic temperature, T₀, of 167 K. Over 150 mW of average power is measured per facet for a duty cycle of 6%. Simulation of the average power output reveals a thermal resistance of 12 K/W for epilayer-up mounted ridges. reprint
513.	Low-Pressure Metal Organic Chemical Vapor Deposition Growth of InAsSbP Based Materials for Infrared Laser Applications M. Razeghi 15th Annual Solid State and Diode Laser Technology Review (SSDLTR), Albuquerque, NM; Technical Digest MIR1-- June 3, 2002
514.	High power InAsSbP based electrical injection laser diodes emitting between 3-5 μm W. Zhang and M. Razeghi 15th Annual Solid State and Diode Laser Technology Review (SSDLTR), Albuquerque, NM; Technical Digest MIR1-- June 3, 2002
515.	High-Power (~9 μm) Quantum Cascade Lasers S. Slivken, Z. Huang, A. Evans, and M. Razeghi Virtual Journal of Nanoscale Science and Technology 5 (22)-- June 3, 2002reprint
516.	Optoelectronics: Learning From Nature M. Razeghi and S. Slivken Business Briefing: Global Optical Communications-- June 1, 2002
517.	Short Wavelength Solar-Blind Detectors: Status, Prospects, and Markets M. Razeghi IEEE Proceedings, Wide Bandgap Semiconductor Devices: The Third Generation Semiconductor Comes of Age 90 (6)-- June 1, 2002 Recent advances in the research work on III-nitride semiconductors and Al_xGa_1-xN materials in particular has renewed the interest and led to significant progress in the development of ultraviolet (UV) photodetectors able to detect light in the mid- and near-UV spectral region (λ∼200-400 nm). There have been a growing number of applications which require the use of such sensors and, in many of these, it is important to be able to sense UV light without detecting infrared or visible light, especially from the Sun, in order to minimize the chances of false detection or high background. The research work on short-wavelength UV detectors has, therefore, been recently focused on realizing short-wavelength "solar-blind" detectors which, by definition, are insensitive to photons with wavelengths longer than ∼285 nm. In this paper the development of Al_xGa_1-xN-based solar-blind UV detectors will be reviewed. The technological issues pertaining to material synthesis and device fabrication will be discussed. The current state-of-the-art and future prospects for these detectors will be reviewed and discussed. reprint
518.	Advanced InAs/GaSb Superlattice Photovoltaic Detectors for Very-Long Wavelength Infrared Applications Y. Wei, A. Gin, M. Razeghi, and G.J. Brown Applied Physics Letters 80 (18)-- May 6, 2002 We report on the temperature dependence of the photoresponse of very long wavelength infrared type-II InAs/GaSb superlattice based photovoltaic detectors grown by molecular-beam epitaxy. The detectors had a 50% cutoff wavelength of 18.8 μm and a peak current responsivity of 4 A·W^-1 at 80 K. A peak detectivity of 4.5×10¹⁰ cm· Hz^½·W^-1 was achieved at 80 K at a reverse bias of 110 mV. The generation–recombination lifetime was 0.4 ns at 80 K. The cutoff wavelength increased very slowly with increasing temperature with a net shift from 20 to 80 K of only 1.2 μm reprint
519.	Future of Al_xGa_1-xN Materials and Device Technology for Ultraviolet Photodetectors P. Kung, A. Yasan, R. McClintock, S. Darvish, K. Mi, and M. Razeghi SPIE Conference, San Jose, CA, Vol. 4650, pp. 199-- May 1, 2002 Design of the photodetector structure is one of the key issues in obtaining high performance devices; especially the thickness of the intrinsic region for p-i-n photodiodes is a crucial value and needs to be optimized. We compare the performance of the p-i-n photodiodes with different widths for the depletion region, which shows a trade-off between speed and responsivity of the devices. reprint
520.	Characteristics of high quality p-type Al_xGa_1-xN/GaN superlattices A. Yasan, R. McClintock, S.R. Darvish, Z. Lin, K. Mi, P. Kung, and M. Razeghi Applied Physics Letters 80 (12)-- March 18, 2002 Very-high-quality p-type Al_xGa_1–xN/GaN superlattices have been grown by low-pressure metalorganic vapor-phase epitaxy through optimization of Mg flow and the period of the superlattice. For the superlattice with x = 26%, the hole concentration reaches a high value of 4.2×10¹⁸ cm^–3 with a resistivity as low as 0.19 Ω · cm by Hall measurement. Measurements confirm that superlattices with a larger period and higher Al composition have higher hole concentration and lower resistivity, as predicted by theory. reprint
521.	High Detectivity GaInAs/InP Quantum Well Infrared Photodetectors Grown on Si Substrates J. Jiang, C. Jelen, M. Razeghi and G.J. Brown IEEE Photonics Technology Letters 14 (3)-- March 1, 2002 In this letter, we report an improvement in the growth and the device performance of GaInAs-InP quantum well infrared photodetectors grown on Si substrates. Material growth techniques, like low-temperature nucleation layers and thick buffer layers were used to grow InP on Si. An in situ thermal cycle annealing technique was used to reduce the threading dislocation density in the InP-on-Si. Detector dark current was reduced 2 orders of magnitude by this method. Record high detectivity of 2.3 × 10⁹ cm·Hz^½·W^-1 was obtained for QWIP-on-Si detectors in the 7-9 μm range at 77 K reprint
522.	Type-II InAs/GaSb Superlattices and Detectors with Cutoff Wavelength Greater Than 18 μm M. Razeghi, Y. Wei, A. Gin, G.J. Brown and D. Johnstone Proceedings of the SPIE, San Jose, CA, Vol. 4650, 111 (2002)-- January 25, 2002 The authors report the most recent advances in Type-II InAs/GaSb superlattice materials and photovoltaic detectors. Lattice mismatch between the substrate and the superlattice has been routinely achieved below 0.1%, and less than 0.0043% as the record. The FWHM of the zeroth order peak from x-ray diffraction has been decreased below 50 arcsec and a record of less than 44arcsec has been achieved. High performance detectors with 50% cutoff beyond 18 micrometers up to 26 micrometers have been successfully demonstrated. The detectors with a 50% cut-off wavelength of 18.8 micrometers showed a peak current responsivity of 4 A/W at 80K, and a peak detectivity of 4.5¹⁰ cm·Hz^½·W^-1 was achieved at 80K at a reverse bias of 110 mV under 300 K 2(pi) FOV background. Some detectors showed a projected 0% cutoff wavelength up to 28~30 micrometers . The peak responsivity of 3Amp/Watt and detectivity of 4.25¹⁰ cm·Hz^½·W^-1 was achieved under -40mV reverse bias at 34K for these detectors. reprint
523.	Development of Quantum Cascade Lasers for High Peak Output Power and Low Threshold Current Density S. Slivken and M. Razeghi Solid State Electronics 46-- January 1, 2002 Design and material optimization are used to both decrease the threshold current density and increase the output power for quantum cascade lasers. Waveguides are designed to try and minimize free-carrier and surface-plasmon absorption. Excellent material characterization is also presented, showing excellent control over layer thickness, interface quality, and doping level. Experiments are done to both optimize the injector doping level and to maximize the output power from a single aperture. At 300 K, a threshold current density as low as 1.8 kA/cm² is reported, along with peak powers of approximately 2.5 W. Strain-balanced lasers are also demonstrated at λnot, vert, similar5 μm, exhibiting threshold current densities<300 A/cm² at 80 K. These values represent the state-of-the-art for mid-infrared lasers with λ>4 μm reprint
524.	280 nm UV LEDs Grown on HVPE GaN Substrates A. Yasan, R. McClintock, K. Mayes, S.R. Darvish, P. Kung, M. Razeghi, and R.J. Molnar Opto-Electronics Review, 10 (4)-- January 1, 2002 We report on the enhancement of optical and electrical properties of 280 nm UV LEDs using low dislocation density HVPE-grown GaN substrate. Compared with the same structure grown on sapphire, these LEDs show ~30% reduction in current-voltage differential resistance, ~15% reduction in turn-on voltage, more than 200% increase in output power slope efficiency and saturation at higher currents. Lower density of defects due to higher material quality and better heat dissipation are believed to be the reason behind these improvements. reprint
525.	Crystallographic Growth Models of Wurtzite-Type Thin Films on 6H-SiC H. Ohsato, K. Wada, T. Kato, C.J. Sun, and M. Razeghi Materials Science Forum Vol. 389-393, no. 2, pp. 1489-1492.-- January 1, 2002 Epitaxial growth of GaN has been tried using various kinds of substrates so far. Of all the substrate, Al₂O₃ has been widely used for the GaN growth. Besides Al₂O₃, SiC is also expected as one of the most suitable substrates for the GaN growth, since SiC has a small mismatch in the lattice parameters with GaN and has good thermal stability under controlled atmospheres during the GaN growth. Both 6H-SiC and GaN having wurtzite structure belong to the same space group (P6₃mc). The lattice parameters are as follows: a=3.08, c=15.08 Å for 6H-SiC and a=3.19, c=5.18 Å for GaN. SiC has two opposite surface polarities along [001] direction. The main objective of our research was to establish a crystallographic growth model of GaN on the (001)6H-SiC with different polarities of Si and C surfaces.

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