Center for Quantum Devices - Journal Articles and Conference Proceedings

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501.	High power InAsSbP based electrical injection laser diodes emitting between 3-5 μm W. Zhang and M. Razeghi -- June 3, 2002
502.	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
503.	Optoelectronics: Learning From Nature M. Razeghi and S. Slivken -- June 1, 2002
504.	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
505.	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
506.	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
507.	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
508.	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
509.	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
510.	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
511.	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
512.	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.
513.	Type-II Binary Superlattices for Infrared Detector M. Razeghi, H. Mohseni and G.J. Brown Journal of the Korean Physical Society 39-- December 1, 2001 III-V quantum wells and superlattices based on InAs/GaSb/AlSb, and related compounds have attracted many attentions due to their unique band alignments and physical properties. Recently, novel electronic and optoelectronic heterostructures have been proposed from this material system for hundred gigahertz logic circuits, terahertz transistors, RTDs, infrared lasers, and infrared detectors. In this paper we will describe the ongoing research at the Center for Quantum Devices to develop the theory, modeling, growth, characterization, and device fabrication techniques for this material system. We have demonstrated the rst uncooled infrared detectors from type-II superlattices. The measured detectivity is more than 1 x 10⁸ cm·Hz^½/W at 10.6 μm at room temperature which is higher than the commercially available uncooled photon detectors at similar wavelength. In parallel, we have demonstrated the rst high-performance p-i-n type-II photodiode in the very long wavelength infrared (VLWIR) range operating at T = 80 K. The devices with cuto wavelength of 16 μm showed a responsivity of 3.5 A/W at 80 K leading to a detectivity of 1.51 x 10¹⁰ cm·Hz^½/W. Similar devices with cutoff wavelengths up to 25 μm was demonstrated at 80 K. To enhance this technology further, we plan to move from quantum wells to quantum wire and quantum dots.
514.	Quantum Dots of InAs/GaSb Type-II Superlattice for Infrared Sensing M. Razeghi, Y. Wei, A. Gin and G.J. Brown Materials Research Society Fall Meeting, Boston, MA; MRS Symposium Proceedings, Vol. 692 (H3.1)-- November 26, 2001 Throughout the past years, significant progress has been made in Type-II (InAs/GaSb) photovoltaic detectors in both LWIR and VLWIR ranges. BLIP performance at 60K for 16 μm photovoltaic Type-II detectors has been successfully demonstrated for the first time. The detectors had a 50% cut-off wavelength of 18.8 μm and a peak current responsivity of 4 A/W at 80K. A peak detectivity of 4.5×1010cm·Hz1/2/W was achieved at 80K at a reverse bias of 110mV. Detectors of cutoff wavelength up to 25μm have been demonstrated at 77K. The great performance of single element detectors appeals us to lower dimensional structures for both higher temperature performance and possible wavelength tunability. Simple calculations show that quantum effects will become significant when the lateral confinement is within tens of nanometers. The variation of applied gate voltage will move the electron and hole energy levels unevenly. The cutoff wavelength of the superlattice will vary accordingly. Auger recombination will also decrease and higher temperature operation becomes possible. In this talk, the latest results will be discussed.
515.	High Power 3-12 μm Infrared Lasers: Recent Improvements and Future Trends M. Razeghi, S. Slivken, A. Tahraoui, A. Matlis, and Y.S. Park Physica E: Low-Dimensional Systems and Nanostructures 11 (2-3)-- October 1, 2001 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
516.	Long Wavelength Type-II Photodiodes Operating at Room Temperature H. Mohseni and M. Razeghi IEEE Photonics Technology Letters 13 (5)-- May 1, 2001 The operation of uncooled InAs-GaSb superlattice photodiodes with a cutoff wavelength of λc=8 μm and a peak detectivity of 1.2 × 10⁸ cm·Hz^½/W at zero bias is demonstrated. The detectivity is similar to the best uncooled HgCdTe detectors and microbolometers. However, the R0A product is more than two orders of magnitude higher than HgCdTe and the device is more than four orders of magnitude faster than microbolometers. These features combined with their low 1/f noise and high uniformity make these type-II photodiodes an excellent choice for uncooled high-speed IR imaging arrays reprint
517.	High Performance InAs/GaSb Superlattice Photodiodes for the Very Long Wavelength Infrared Range H. Mohseni, M. Razeghi, G.J. Brown, Y.S. Park Applied Physics Letters 78 (15)-- April 9, 2001 We report on the demonstration of high-performance p-i-n photodiodes based on type-II InAs/GaSb superlattices with 50% cut-off wavelength λ_c = 16 μm operating at 80 K. Material is grown by molecular beam epitaxy on GaSb substrates with excellent crystal quality as evidenced by x-ray diffraction and atomic force microscopy. The processed devices show a current responsivity of 3.5 A/W at 80 K leading to a detectivity of ∼ 1.51×10¹⁰ cm·Hz^½/W. The quantum efficiency of these devices is about 35% which is comparable to HgCdTe detectors with a similar active layer thickness. reprint
518.	Miniaturization: enabling technology for the new millennium M. Razeghi and H. Mohseni SPIE International Conference on Solid State Crystals, Zakopane, Poland, -- April 1, 2001 The history of semiconductor devices has been characterized by a constant drive toward lower dimensions in order to increase integration density, system functionality and performance. However, this is still far from being comparable with the performance of natural systems such as human brain. The challenges facing semiconductor technologies in the millennium will be to move toward miniaturization. The influence of this trend on the quantum sensing of infrared radiation is one example that is elaborated here. A new generation of infrared detectors has been developed by growing layers of different semiconductors with nanometer thicknesses. The resulted badgap engineered semiconductor has superior performance compared to the bulk material. To enhance this technology further, we plan to move from quantum wells to quantum wire and quantum dots. reprint
519.	High performance quantum cascade lasers (~11 μm) operating at high temperature (T>= 425K) A. Tahraoui, A. Matlis, S. Slivken, J. Diaz, and M. Razeghi Applied Physics Letters 78 (4)-- January 22, 2001 We report record-low threshold current density and high output power for λ ∼ 11 μm Al_0.48In_0.52As/Ga_0.47In_0.53As quantum cascade lasers operating up to 425 K. The threshold current density is 1.1, 3.83, and 7.08 kA/cm² at 80, 300, and 425 K, respectively, for 5 μs pulses at a 200 Hz repetition rate. The cavity length is 3 mm with a stripe width of 20 μm. The maximum peak output power per facet is 1 W at 80 K, 0.5 W at 300 K, and more than 75 mW at 425 K. The characteristic temperature of these lasers is 174 K between 80 and 300 K and 218 K in the range of 300–425 K. reprint
520.	High Performance Quantum Cascade Lasers Grown by Gas-Source Molecular Beam Epitaxy M. Razeghi, S. Slivken, A. Tahraoui and A. Matlis SPIE Conference, San Jose, CA, -- January 22, 2001 Recent improvements in quantum cascade laser technology have led to a number of very impressive results. This paper is a brief summary of the technological development and state-of- the-art performance of quantum cascade lasers produced at the Center for Quantum Devices. Laser design will be discussed, as well as experimental details of device fabrication. Room temperature QCL operation has been reported for lasers emitting between 5 - 11 μm, with 9 - 11 μm lasers operating up to 425 K. We also demonstrate record room temperature peak output powers at 9 and 11 μm(2.5 W and 1 W respectively) as well as record low 80 K threshold current densities (250 A/cm²) for some laser designs. Finally, some of the current limitations to laser efficiency are mentioned, as well as a means to combat them. reprint
521.	Quantum Dot Intersubband Photodetectors C. Jelen, M. Erdtmann, S. Kim, and M. Razeghi SPIE Conference, San Jose, CA, -- January 22, 2001 Quantum dots are recognized as very promising candidates for the fabrication of intersubband photodetectors in the infrared spectral range. At present, material quality is making rapid progress and some devices have been demonstrated. Examples of mid-infrared quantum dot intersubband photodetectors are presented along with device design and data analysis. Nonetheless, the performance of these devices remains less than comparable quantum well intersubband photodetectors due to difficulties in controlling the quantum dot size and distribution during epitaxy. reprint
522.	Monolithic Integration of GaInAs/InP Quantum Well Infrared Photodetectors on Si Substrate M. Erdtmann and M. Razeghi SPIE Conference, San Jose, CA, -- January 22, 2001 Using low-pressure metalorganic chemical vapor deposition, we have grown GaInAs/InP QWIP structures on GaAs-coated Si substrate. First, the procedure to optimize the epitaxy of the InP buffer layer on Si substrate is given. Excellent crystallinity and a mirror-like surface morphology were obtained by using both a two-step growth process at the beginning of the InP buffer layer growth and several series of thermal cycle annealing throughout the InP buffer layer growth. Second, results of fabricated GaInAs/InP QWIPs on Si substrate are presented. At a temperature of 80 K, the peak response wavelength occurs at 7.4 μm. The responsivities of QWIPs on both Si and InP substrates with identical structures are equal up to biases of 1.5 V. At a bias of 3 V, the responsivity of the QWIPs on Si substrate is 1.0 A/W. reprint
523.	High Performance Type-II InAs/GaSb Superlattice Photodiodes H. Mohseni, Y. Wei, and M. Razeghi SPIE Conference, San Jose, CA, -- January 22, 2001 We report on the demonstration of high performance p-i-n photodiodes based on Type-II InAs/GaSb superlattices operating in the very long wavelength infrared (VLWIR) range at 80 K. Material is grown by molecular beam epitaxy on GaSb substrates with excellent crystal quality as evidenced by x-ray diffraction and atomic force microscopy. The processed devices with a 50% cutoff wavelength of λ_c equals 22 μm show a peak current responsivity about 5.5 A/W at 80 K. The use of binary layers in the superlattice has significantly enhanced the uniformity and reproducibility of the energy gap. The 90% to 10% cut-off energy width of these devices is on the order of 2 kT which is about four times smaller compared to the devices based on InAs/Ga1-xInxSb superlattices. Similar photovoltaic devices with cut-off wavelengths up to 25 μm have been measured at 80 K. Our experimental results shows excellent uniformity over a three inch wafer area, indicating the possibility of VLWIR focal plane arrays based on Type-II superlattices. reprint
524.	Al_xGa_1-xN Materials and Device Technology for Solar Blind Ultraviolet Photodetector Applications R. McClintock, P. Sandvik, K. Mi, F. Shahedipour, A. Yasan, C. Jelen, P. Kung, and M. Razeghi SPIE Conference, San Jose, CA, Vol. 4288, pp. 219-- January 22, 2001 There has been a growing interest for the development of solar blind ultraviolet (UV) photodetectors for use in a variety of applications, including early missile threat warning, flame monitoring, UV radiation monitoring and chemical/biological reagent detection. The Al_xGa_1-xN material system has emerged as the most promising approach for such devices. However, the control of the material quality and the device technology are still rather immature. We report here the metalorganic chemical vapor deposition, the n-type and the p-type doping of high quality Al_xGa_1-xN thin films on sapphire substrates over a wide range of Al concentration. reprint
525.	Novel Sb-based Alloys for Uncooled Infrared Photodetector Applications M. Razeghi SPIE Conference, San Jose, CA, -- January 22, 2001 We report on the growth and characterization of InSbBi, InTlSb, InTlP, and the quaternary alloys for uncooled long- wavelength infrared photodetector applications. The layers were grown on InSb and GaAs substrates by low-pressure metalorganic chemical vapor deposition. The incorporation of Bi and Tl in InSb was investigated with high-resolution x-ray diffraction, energy dispersive x-ray analysis, and optical photoresponse measurements. We also demonstrate the photodetectors fabricated from the grown InSbBi and InTlSb alloys. InSb_0.96Bi_0.04 photoconductive detectors exhibited a responsivity of 3.2 V/W at 77 K. The estimated Johnson noise limited detectivityat 7 micrometers was 1.7 X 10⁸ cm·Hz^½/W at 77 K. A room temperature operating InSb_0.95Bi_0.05 photodetector was also demonstrated.Photoresponse up to 12 micrometers was achieved at 300 K. The responsivity and Johnson noise-limited detectivity at 10.6 μm were 1.9 mV/W and 1.2 X 10⁶ cm·Hz^½/W, respectively. Photoresponse up to 15 μm was achieved at 300 K from quaternary InTlAsSb and InBiAsSb alloys. reprint

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