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376.  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
 
377.  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.
 
378.  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/InxGa1-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
 
379.  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
 
380.  Very high quality p-type AlxGa1-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 AlxGa1−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 A0.1Ga0.9N/GaN superlattice is estimated to be not, vert, similar 125 and 3 meV respectively. reprint
 
381.  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·Hz½/W at 11 μm at room temperature, while photodiodes show a zero-bias detectivity of 1.2x108 cm·Hz½/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·Hz½/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.
 
382.  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
 
383.  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.
 
384.  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
 
385.  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
 
386.  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 Hz½/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
 
387.  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
 
388.  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
 
389.  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
 
390.  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
 
391.  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
 
392.  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
 
393.  Low-Pressure Metal Organic Chemical Vapor Deposition Growth of InAsSbP Based Materials for Infrared Laser Applications
M. Razeghi
-- June 3, 2002
 
394.  High power InAsSbP based electrical injection laser diodes emitting between 3-5 μm
W. Zhang and M. Razeghi
-- June 3, 2002
 
395.  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
 
396.  Optoelectronics: Learning From Nature
M. Razeghi and S. Slivken
-- June 1, 2002
 
397.  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 AlxGa1-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 AlxGa1-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
 
398.  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· Hz½·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
 
399.  Future of AlxGa1-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
 
400.  Characteristics of high quality p-type AlxGa1-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 AlxGa1–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
 

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