IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 6, JUNE /$ IEEE

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1 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 6, JUNE Long-Wave InAs/GaSb Superlattice Detectors Based on nbn and Pin Designs Arezou Khoshakhlagh, Stephen Myers, HaSul Kim, Elena Plis, Nutan Gautam, Sang Jun Lee, Sam Kyo Noh, L. Ralph Dawson, and Sanjay Krishna, Senior Member, IEEE Abstract The development of type-ii InAs/GaSb superlattice (SL) detectors with nbn and pin designs for the long-wave infrared (LWIR) spectral region is discussed. The dependence of dark current density and responsitivity of the pin photodetectors on doping type and level is investigated, and it is shown that dark current density decreases while responsivity and detectivity increase by p-doping the absorbing region of pin detectors. Comparison of optical and electrical properties of SL photodetectors based on the nbn and pin designs is reported. nbn devices have higher specific detectivity (D ), responsivity, and lower dark current density as compared to the pin detectors. The decrease in dark current in nbn devices is due to suppression of Shockley Reed Hall and surface leakage currents. A specific detectivity (D ) of cm Hz 1 2 W 1 at 0.1 V, a responsivity of 1.28 A/W and a quantum efficiency of 21.3% under 0.2 V biasing at 77 K and 7 m, assuming unity gain, was obtained in the nbn device. Index Terms InAs/GaSb type-ii superlattices, infrared detectors, longwave detector, nbn detector, pin detector. I. INTRODUCTION T HE InAs/GaSb type-ii superlattice (SL) technology has recently shown significant development in infrared (IR) technology and proven itself as a promising competitive technology to the state of the art mercury cadmium telluride (MCT) and the quantum well photoconductive detector systems [1] [3]. One of the main advantages of this system lies in the fact that the effective bandgap of the SL can be tailored over a wide range m m by varying the thicknesses of the two mid bandgap constituent materials, namely GaSb and InAs. Moreover, the larger electron effective mass in these engineered one dimensional crystals helps to reduce tunneling currents. Large splitting between heavy-hole and light-hole valence subbands due to strain in the SLs contributes to the suppression Manuscript received August 28, 2009; revised November 16, 2009, December 23, 2009, and January 11, Current version published March 12, This work is based on research supported by AFRL Contract FA C-0171 and KRISS-UNM Global Research Laboratory Grant. A. Khoshakhlagh, S. Myers, H. Kim, E. Plis, N. Gautam, L. R. Dawson, and S. Krishna are with the Center for High Technology Materials, Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM USA ( karezou@unm.edu; stephenamyers@gmail.com; hasul@chtm.unm.edu; a1ien@chtm.unm.edu; nutan.iitk@gmail.com; rdawson@chtm.unm.edu; skrishna@chtm.unm.edu). S. J. Lee and S. K. Noh are with Korea Research Institute of Standards and Science (KRISS), Daejeon , South Korea ( sjlee@kriss.re.kr; sknoh@kriss.re.kr). Color versions of one or more of the figures in this paper are available online at Digital Object Identifier /JQE Fig. 1. Schematic of nbn design. Majority carriers (electrons) are blocked by the barrier and minority carriers (holes) are the source of current. of Auger recombination. SL based IR detectors have demonstrated high quantum efficiency [4], high temperature operation [5], and are suitable for incorporation in focal plane arrays (FPA) by tapping into the mature III-V based growth and fabrication processes [6]. Most of the present day SL photodetectors are based on the pin photodiode design. In focal plane arrays based on pin diodes, pixels are separated from the their neighbor pixels by an etched mesa. During the mesa isolation process, the periodic nature of the crystal structure ends abruptly at the mesa lateral surface. Disturbance of the periodic potential function due to a broken crystal lattice leads to allowed electronic quantum states within the energy bandgap of SL resulting in large surface leakage currents. The suppression of these currents by using a stable passivation layer for the etched mesa surface for the SL photodiodes is one of the primary limitations of the SL based technology. A class of IR detectors named nbn has shown promising results in eliminating the currents associated with Shockley Read Hall (SRH) centers and mesa lateral surface imperfections, which have resulted in an increase of the operating temperature [7] as compared to the pin design. This so-called nbn structure consists of a n-type narrow bandgap contact and absorber layers separated by a nm-thick wide bandgap barrier layer. A schematic of ideal nbn structure is shown in Fig. 1. Implementation of the nbn design for InAs/GaSb midwave infrared (MWIR) SL single element and FPAs have been reported [3], [8], [9], but to date, little work has been reported on the performance of long-wave infrared (LWIR) nbn based devices [10]. LWIR SL system is a residually n-type system due to thicker layers of residually n-type InAs layers as compared to the residually p-type GaSb layers. Therefore, the dopant material and its concentration is an important parameter in long-wave (LW) InAs/GaSb type-ii SL design and growth, that can affect the optical and electrical properties of SLs structures. Beryllium (Be) doping the InAs layers has shown to be an effective method in /$ IEEE

2 960 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 6, JUNE 2010 decreasing the dark current by lowering the diffusion, generation recombination (GR) and tunneling currents and increase the quantum efficiency of the device by switching to high mobility minority electron concentration [11]. In the present work, investigation of LWIR pin detector and the influence of absorber p-doping on the optical and electrical properties of the devices is presented. The optical and electrical properties of LWIR nbn based detectors are also reported and compared to those of optimized p-doped pin detectors. II. GROWTH OF LONG-WAVE InAs/GaSb SUPERLATTICES In InAs/GaSb SL, two types of interfaces can be grown along the [001] growth direction, the InSb-like or GaAs-like interface. The lattice constant of InSb (GaAs) is much larger (smaller) than that of the GaSb substrate. Therefore, large compressive (tensile) strain can build up inside SLs structure that affects the structural, optical and electrical properties of the SL dramatically. Development of an optimized growth procedure for the strain-balanced SL with well-ordered constituent and interfacial layers is critical for the realization of a photodetector operating in the LWIR range (8 12 m) with large absorption coefficient and reduced dark current. For the purpose of strain optimization in the LWIR SL structure, two sets of samples with 60 periods of SL with the same composition (13 MLs InAs/7 MLs GaSb) and different methods of InSb interface formation were investigated. In the first method, an InSb layer was inserted between InAs and GaSb layers. In the second method, the insertion of an InSb like interface by using group V soak times was investigated. The insertion of an InSb layer in the SL structure resulted in the lowest full-width at half-maximum (FWHM) for the first order satellite peak and lowest lattice mismatch between the SL and the GaSb substrate from XRD as compared to the structures grown with insertion of group V soak times. Detailed growth and interface optimization of LW SLs is not described here and can be found elsewhere [12]. High resolution X-ray diffraction (HXRD) scan and cross-sectional scanning transmission electron microscopy (STEM) of the grown structures are shown in Fig. 2(a) and (b), respectively. X-ray diffraction rocking curve reveals intense satellite peaks attesting a good crystalline quality of the layers and the zeroth-order SL peak position indicates that the SL is practically lattice matched to the GaSb substrate. STEM image also shows sharp and well defined interfaces for SL structure which is an indication of high quality growth. To study the influence of p-doping of the absorbing region of pin SL detectors on the device performance, a set of three pin detectors along with one nbn detector were grown. To enable device comparisons, all four samples had exact same thicknesses for the absorbing region. Devices were grown on Te-doped epi-ready (100) GaSb substrates using a solid source molecular beam epitaxy VG-80 system. The system was equipped with SUMO cells for gallium and indium, a standard effusion cell for aluminum and cracker cells for antimony and arsenic. Detector based on nbn design consisted of a 380 nm bottom contact layer formed by 13 MLs InAs:Si 4 10 cm 0.75 ML InSb 7 MLs GaSb SL. Then a 1.9 m-thick nonintentionally doped (n.i.d.) absorber Fig. 2. (a) High resolution XRD of pin detector; (b) cross-sectional STEM image of nbn detector. Top contact and active region are formed by 13 ML InAs/7GaSb SL, Al GaSb barrier and GaSb spacer are also shown. region formed by 13 MLs InAs/0.75 ML InSb/7 MLs GaSb SL was grown followed by a 100-nm-thick Al GaSb barrier layer. The Al GaSb barrier layer was capped with a 20-nm-thick GaSb spacer to avoid oxidation of the Al during the processing steps. The structure was terminated by a 125-nm-thick n-type cm top contact layer with the same composition as the bottom contact layer. Detectors based on pin design consisted of a 473 nm thick bottom contact layer formed by 13 MLs InAs:Si cm 0.75 ML InSb 7 MLs GaSb SL followed by 250-nm-thick doping graded layers of 13 MLs InAs:Si/0.75 ML InSb/7 MLs GaSb SL to achieve doping concentration of cm before the absorbing layer. Then a 1.9 m thick absorber formed by 13 MLs InAs/0.75 ML InSb/7 MLs GaSb SL was grown followed by 250-nm-thick p-doping graded layers. The structure was terminated by a 125 nm-thick p-type cm top contact layer with the same composition as the bottom contact layer. The absorber region doping level was varied (Be-doped: cm, Be-doped: cm and undoped) during the growth of the three pin detectors. The

3 KHOSHAKHLAGH et al.: LONG-WAVE InAs/GaSb SUPERLATTICE DETECTORS BASED ON nbn AND PIN DESIGNS 961 Fig. 3. The heterostructure schematics of the LWIR (a) pin; (b) nbn SL structures. Fig. 4. Schematic of (a) conventionally defined mesa; (b) shallow etched isolation nbn device. In the latter case, the active area is defined by the diffusion length (DL) of the minority carriers (holes). heterostructure schematics of the pin and nbn structures are presented in Fig. 3(a) and (b), respectively. III. PROCESSING OF PIN AND NBN PHOTODETECTORS The devices were processed using m square mesas with circle apertures with varying radii from 25 to 300 m. Processing was initiated by standard optical photolithography for top contact metal deposition. Then, a shallow isolation etch was undertaken using inductively coupled plasma (ICP) dry etch to the top of the barrier layer for the nbn structure with an etch depth of 125 nm. Thus, the active absorber layer underneath is not exposed. Then, ICP dry etch to the middle of the bottom contact layer was performed for both nbn and pin structures. SiN passivation was performed for pin detectors. Finally, samples were patterned and bottom contact metal was deposited. Ti/Pt/Au (500/500/3000 ) were used as contact metals for both top and bottom contacts. Schematics of processed pin and nbn structures are shown in Fig. 4(a) and (b). Unlike a conventional photodiode processing [see Fig. 4(a)], the size of the device with the nbn design is not defined by dimensions of etched but confined by a lateral diffusion length of minority carriers (holes), as illustrated in Fig. 4(b). IV. CHARACTERIZATION The bandgap of 60 periods of the 13 MLs of InAs and 7 MLs of GaSb SL material system was first determined through room Fig. 5. (a) Absorbance as a function of wavelength. The cut-off wavelength was found to be 8 m (300 K). (b) Spectral response of nbn structure. temperature absorption measurements, which were performed using a Nicolet-870 Nexus Fourier transform infrared (FTIR) spectrometer and the reflectivity module associated with it. The reflectance of the sample was calculated as ratio between the reflected signals measured from the sample and a reference substrate (n-type GaSb). In order to eliminate the transmission component from the consideration, a thin layer of gold (50 nm thick) was deposited on the backside of both the sample and the reference substrate. Thus, the absorbance ( ) as a function of wavelength is calculated using, where is the measured two pass reflectance of the sample. The representative absorption spectrum is shown in Fig. 5(a). The cut-off wavelength (defined as the wavelength where the response went to zero) was found to be 8 m (at 300 K). Spectral measurements of the pin and nbn detectors were performed using a Nicolet 670 FTIR spectrometer and a Keithley 428 preamplifier. Relative spectral response was obtained by dividing the photocurrent of the SL detectors with that obtained using a calibrated [13] deuterated triglycine sulfate (DTGS) thermal detector. The relative spectral response of nbn structure as a function of wavelength is shown in Fig. 5(b). The spectral response of pin structure is similar to the nbn detector since both have the same absorbing region. The data

4 962 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 6, JUNE 2010 Fig. 6. Dark current density at 77 K for nbn and pin structures. Forward bias in nbn design is defined where negative bias is applied on the top of device and reverse bias in pin design is defined where negative bias is applied on the top of device. clearly shows cutoff wavelength of 8 m and is in a good agreement with the reflectivity measurements. Current voltage measurements were obtained using a semiconductor parameter analyzer. Fig. 6 presents the dark current density of pin and nbn structures at 77 K. The data shows that the dark current density of the pin detectors decreases with p-doping the InAs layers in the absorbing region. The lowest dark current density is associated with the sample which the Be doping concentration in InAs layers is cm. In this comparison we neglect the effect of surface leakage currents since all three pin samples were identically processed and passivated. The main dark current components in these detectors are diffusion, generation recombination and tunneling current. By increasing the doping level, diffusion current decreases. The generation recombination current also decreases due to decrease in depletion width. Thus, total dark current density associated with diffusion and generation recombination decreases up to a certain doping concentration ( cm Be doped) but as the doping concentration increases more, the maximum electric field across the depletion region increases which causes the tunneling probability to increase. This can explain the larger dark current density for the cm Be doped sample compared to the n.i.d sample at bias points larger than 0.35 V. Detailed dark current mechanisms in the Be-doped pin detectors can be found in [11]. The optimized pin sample in terms of dark current density is then compared with the nbn detector. Dark current density in ( cm Be doped) pin structure is (0.08 A/cm at 100 mv) as compared to the nbn based design (0.05 A/cm at 100 mv). Dark current density measurements of the nbn design were measured with a 300 K background while the pin dark current density measurements are performed with a cold shield. Deeply etched nbn devices [14] also show lower dark current density than the undoped pin devices. The lower dark current density in deeply ethced nbn design is associated with a reduction of SRH centers due to smaller depletion region as compared to undoped pin devices. Therefore, lower dark curent density of shallow etched nbn devices as compared to pin devices is attributed to reduction of both SRH centers and mesa latera surface imperfection. In order to completely eliminate the dark current associated with SRH centers, an optimized barrier with zero valence band offset is required. In the nbn structures used for this study, the presence of small valence band discontinuity in the structure, results in formation of small depletion region thus there is dark current component due to SRH centers. nbn structure, could also have lateral diffusion of minority carriers (holes), which is ignored in this analysis [15]. Responsivity and specific detectivity were measured at 77 K using a pour-fill dewar and a Micron M365 calibrated 800 K blackbody source. No antireflection coating was applied on the devices. As is shown in Fig. 7(a), the responsivity of pin detectors increases with cm Be doping of the photodiode absorbing region. Further increase in the doping concentration cm leads to a drop in responsitivity of pin photodiodes. To understand this behavior qualitatively, it s worth noticing that the responsivity of a photodetector is the number of collected carriers per incident photon. Therefore, it is proportional to the ratio of photo-carriers leaving the absorbing region and photo-carriers recombining within the absorbing region. When the absorption region is Be doped, the minority carriers switch to high mobility electrons as compared to the nonintentionally doped sample where the minority carriers are holes. The rate that carriers leave the absorbing region is faster in Be doped samples as compared to n.i.d sample. Therefore, the probability of carrier recombination decreases and leads to higher responsivity. However, at higher Be doping concentrations cm, mobility of minority carriers decreases due to the increase in scattering from the dopants. Fig. 7(a) also shows that nbn device has a higher responsivity as compared to the pin devices. Photodiodes based on nbn design eliminate SRH recombination centers associated with depletion regions which are the main source of recombination mechanisms in pin photodiodes, and therefore, more carriers are extracted from the absorbing region which increases the responsivity of these devices. It is worth mentioning that the responsivity of nbn devices can be improved further with optimizing the barrier band offsets and thickness of these structures. The shot-noise limited spectral detectivity was estimated using of the device where is the responsivity, is the electronic charge, is the temperature of the device, is Boltzmann s constant, is the current density, is the dynamic resistance, and is the diode area. Detectivity measurements for pin and nbn devices are shown in Fig. 7(b). At 77 K, the measurements show that the nbn device has the highest detectivity as compared to the pin devices. The behavior seen in Fig. 7(b) for detectivties of pin and nbn devices is well expected since it is a measure of signal (responsivity) to noise (dark current) ratio. Table I shows summarized values of dark current, responsivity and detectivity of pin and nbn devices. V. SUMMARY AND CONCLUSION The development of nbn and pin based detectors for the LWIR spectral regions using type-ii InAs/GaSb SL was presented. To have a precise comparison, all structures were grown (1)

5 KHOSHAKHLAGH et al.: LONG-WAVE InAs/GaSb SUPERLATTICE DETECTORS BASED ON nbn AND PIN DESIGNS 963 REFERENCES Fig. 7. (a) Responsivity and (b) detectivity measurements of the pin and nbn devices at 77 K; nbn structure has the highest responsivity and detectivity values as compared to pin structures. TABLE I SUMMARY OF DARK CURRENT DENSITY,RESPONSIVITY AND DETECTIVITY OF PIN AND NBN DEVICES MEASURED AT 77 K, 7 m with the same SL design and had a 1.9 m thick absorbing region. It was shown that by p-doping the absorbing region of the pin devices, dark current of the pin photodiodes decreases and the pin responsivity and detectivity increases. Devices based on the nbn design showed higher detectivity and responsivity values as compared to pin devices. These improvements in device characteristics of nbn design as compared to pin design is attributed to reduction of dark current due to suppression of currents associated with SRH centers and surface leakage currents. [1] B.-M. Nguyen, D. Hoffman, Y. Wei, P.-Y. Delaunay, A. Hood, and M. Razeghi, Very high quantum efficiency in type-ii InAs/GaSb superlattice photodiode with cutoff of 12 m, Appl. Phys. Lett., vol. 90, no. 23, p , [2] Y. Wei, A. Hood, H. Yau, A. Gin, M. Razeghi, M. Z. Tidrow, and V. Nathan, Uncooled operation of type-ii InAs/GaSb superlattice photodiodes in the midwavelength infrared range, Appl. Phys. Lett., vol. 86, no. 23, p , [3] A. Khoshakhlagh, J. B. Rodriguez, E. Plis, G. D. Bishop, Y. D. Sharma, H. S. Kim, L. R. Dawson, and S. Krishna, Bias dependent dual band response from InAs/Ga(In)Sb type II strain layer superlattice detectors, Appl. Phys. Lett., vol. 91, no. 26, p , [4] R. Rehm, M. Walther, J. Schmitz, J. Fleissner, F. Fuchs, J. Ziegler, and W. Cabanski, InAs/GaSb Superlattice Focal Plane Arrays for High- Resolution Thermal Imaging, A. Rogalski, E. L. Dereniak, and F. F. Sizov, Eds. Bellingham, WA: SPIE 5957, 2005, p [5] E. Plis, S. J. Lee, Z. Zhu, A. Amtout, and S. Krishna, InAs/GaSb superlattice detectors operating at room temperature,, IEEE J. Sel. Top. Quantum Electron., vol. 12, no. 6, pp , Nov. Dec [6] P.-Y. Delaunay, B. M. Nguyen, D. Hoffman, and M. Razeghi, Highperformance focal plane array based on InAs-GaSb superlattices with a 10-m cutoff wavelength,, IEEE J. Quantum Electron., vol. 44, no. 5, pp , May [7] S. Maimon and G. W. Wicks, nbn detector, an infrared detector with reduced dark current and higher operating temperature, Appl. Phys. Lett., vol. 89, no. 15, p , [8] J. B. Rodriguez, E. Plis, G. Bishop, Y. D. Sharma, H. Kim, L. R. Dawson, and S. Krishna, nbn structure based on InAs/GaSb type-ii strained layer superlattices, Appl. Phys. Lett., vol. 91, no. 4, p , [9] H. S. Kim, E. Plis, J. B. Rodriguez, G. D. Bishop, Y. D. Sharma, L. R. Dawson, S. Krishna, J. Bundas, R. Cook, D. Burrows, R. Dennis, K. Patnaude, A. Reisinger, and M. Sundaram, Mid-IR focal plane array based on type-ii InAs/GaSb strain layer superlattice detector with nbn design, Appl. Phys. Lett., vol. 92, no. 18, p , [10] D. Z.-Y. Ting, C. J. Hill, A. Soibel, S. A. Keo, J. M. Mumolo, J. Nguyen, and S. D. Gunapala, A high-performance long wavelength superlattice complementary barrier infrared detector, Appl. Phys. Lett., vol. 95, no. 2, p , [11] D. Hoffman, B.-M. Nguyen, P.-Y. Delaunay, A. Hood, M. Razeghi, and J. Pellegrino, Beryllium compensation doping of InAs/GaSb infrared superlattice photodiodes, Appl. Phys. Lett., vol. 91, no. 14, p , [12] A. Khoshakhlagh, E. Plis, S. Myers, Y. Sharma, L. Dawson, and S. Krishna, Optimization of InAs/GaSb type-ii superlattice interfaces for long-wave (8 m) infrared detection, J. Crystal Growth, vol. 311, no. 7, pp , 2009, International Conference on Molecular Beam Epitaxy (MBE-XV), The 15th International Conference on Molecular Beam Epitaxy (MBE-XV). [13] J. W. Little, S. P. Svensson, W. A. Beck, A. C. Goldberg, S. W. Kennerly, T. Hongsmatip, M. Winn, and P. Uppal, Thin active region, type II superlattice photodiode arrays: Single-pixel and focal plane array characterization, J. Appl. Phys., vol. 101, no. 4, p , [14] G. Bishop, E. Plis, J. B. Rodriguez, Y. D. Sharma, H. S. Kim, L. R. Dawson, and S. Krishna, nbn detectors based on inas/gasb type-ii strain layer superlattice, J. Vacuum Science and Technology B, vol. 26, no. 3, pp , [15] E. Plis, H. S. Kim, G. Bishop, S. Krishna, K. Banerjee, and S. Ghosh, Lateral diffusion of minority carriers in nbn based type-ii InAs/GaSb strained layer superlattice detectors, Appl. Phys. Lett., vol. 93, no. 12, p , Arezou Khoshakhlagh received the B.S. degree (with honors) and M.S. degree in electrical engineering, in 2004 and 2008 from the University of New Mexico, Albuquerque, where she is currently working toward the Ph.D. degree in optical sciences and engineering. She also has a Ph.D. minor in nano-technology and microsystems from the University of New Mexico. Her research interests include design, molecular beam epitaxy growth and characterization of InAs/ GaSb superlattice IR detectors, GaSb quantum dot and Si-based LED, laser, and solar cells. She is also a Fellow of the NSF sponsored NSMS-IGERT program.

6 964 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 6, JUNE 2010 Stephen Myers received the B.S degree in engineering physics in May 2007 from Tarleton State University, Texas A&M. He was then accepted into the Nanoscience and Microsystems Integrative Graduate Education and Research Traineeship (NSMS IGERT) fellowship at the University of New Mexico, where he is presently working with Prof. Sanjay Krishna. He is currently working on developing infrared detector based on type-ii strain layered superlattices. HaSul Kim is currently pursuing the Ph.D. degree in optical science and engineering at the University of New Mexico. He was at the University of Alabama, Huntsville, and at Brigham Young University prior to joining UNM. He also has extensive industrial experience that he is tapping into as he investigates novel strategies to realize high performance focal plane arrays based on strained layer superlattices. Sam Kyo Noh received the M.Sc. and Ph.D. degrees from Yonsei University, Seoul, Korea, in 1980 and 1986, respectively, both in semiconductor physics. He was a Postdoctoral Researcher at Brown University, Providence, RI, and the Frontier Research Laboratory of RIKEN, Wako, Japan, during In 1989, he joined Korea Research Institute of Standards and Science (KRISS), Daejeon, Korea, as a Group Leader, and is currently a Principal Research Scientist. He was a Visiting Researcher at Electrical and Computer Engineering Department, University of Michigan, Ann Arbor, in 2000, and the University of California at Los Angeles in He is also a PI of the Global Research Laboratory (GRL) on Quantum Detector Technology, which collaborates with the University of New Mexico, Albuquerque. His current research interests include growth and fabrication of nanoscale structures and devices, especially for quantum-dot and superlattice-based far-infrared/terahertz detectors. He has authored or coauthored and presented more than 100 research papers each in journals and conferences. Dr. Noh was awarded the Presidential Medal of Merit (Korean Government) in 2003 and the Academic Achievement Prize (Korean Physical Society) in 2004 in recognition of works on quantum semiconductors. Elena Plis received the Engineering degree from the Kovrov State Technological Academy, Russia, in 2001, the M.S. degree in electrical engineering in 2005 and the Ph.D. degree in electrical engineering in 2007 from the University of New Mexico. She is an Assistant Research Professor at the Center for High Technology Materials at the University of New Mexico. Her present research interests include growth, fabrication and characterization of type-ii InAs/(In,Ga)Sb Strained Layer Superlattice (SLS) IR detectors for MWIR and LWIR spectral regions. She is also interested in chemistry of GaSb-based materials and application of IR sensors for early skin cancer detection. L. Ralph Dawson received the B.S. degree in electrical engineering from the California Institute of Technology, Pasadena, the M.S. and Ph.D. degrees in electrical engineering from the University of Southern California, Los Angeles. He is a Research Professor in the EECE Department, Center for High Technology Materials, University of New Mexico, Albuquerque. He was a Distinguished Member of Technical Staff at Sandia National Laboratories, Albuquerque, and formerly a Member of Technical Staff, Bell Laboratories, Murray Hill, NJ, from 1969 to His research interests are MBE growth of III-V arsenides and antimonides for IR emitters and detectors, monolithic integration of Silicon and III-V device structures, and MBE growth of highly mismatched materials. He has more 185 journal publications, 160 conference presentations, and 12 patents. He is also editor of six proceedings volumes. Nutan Gautam received the B.Sc. (Hons.) in physics and the M.Sc. in physics from Dayalbagh Educational Institute, Agra, India, in 2003 and 2005, respectively, and the M.Tech. (EE/photonics) from the Indian Institute of Technology, Kanpur, India, in July She worked as a scientist in Bhabha Atomic Research Centre, Mumbai, India, from August 2007 to July She joined the Electrical Engineering Department, University of New Mexico, as a graduate student in Fall Since then, she has been working with Prof. Krishna towards the Ph.D. degree. Her research interests are nanostructure semiconductor device modeling, growth and optical characterization. Sang Jun Lee received the B.S., M.S., and Ph.D. degrees in physics from the Kyunghee University, Suwon, Korea, in 1995, 1997, and 2004, respectively. From 1997 to 2002, he was a Researcher at the Center for Electro-Optics, Korea Advanced Institute of Science and Technology, Daejeon. In 2002, He joined the Korea Research Institute of Standards and Science at Daejeon, where he is currently a Senior Research Scientist in at the Center for Advanced Measurement and Instrumentation. In and 2008, he worked as the visiting scientist of the Prof. S. Krishna group at University of New Mexico, Albuquerque. His research interests include the epitaxial growth of the self-assembled quantum dots (SAQD) and type II strained layer superlattices (SLS) with MBE, fabrication of infrared focal plane array using SAQD and SLS structures and hybrid bonding technology. Sanjay Krishna (SM 08) received the Master s degree in physics from the Indian Institute of Technology (IIT) Madras, Chennai, India, in 1996, and the M.S. degree in electrical engineering and the Ph.D. degree in applied physics from the University of Michigan, Ann Arbor, in 1999 and 2001, respectively. In 2001, he joined the University of New Mexico, Albuquerque, as a Tenure Track Faculty Member and is currently an Associate Professor of electrical and computer engineering at the Center for High Technology Materials. His current research interests include growth, fabrication, and characterization of self-assembled quantum dots and type II InAs/InGaSb-based strain layer superlattices for midinfrared detectors. He has authored or coauthored more than 70 peer-reviewed journal articles, more than 40 conference presentations, two book chapters, and holds two issued and five pending patents. Dr. Krishna received the Gold Medal from the IIT Madras in He received the Best Student Paper Award at the 16th North American Conference on Molecular Beam Epitaxy (NAMBE), Banff, AB, Canada, in 1999, the 2002 Ralph E. Powe Junior Faculty Award from Oak Ridge Associated Universities, the 2003 IEEE Outstanding Engineering Award, the 2004 Outstanding Researcher Award from the Electrical and Computer Engineering Department, the 2005 School of Engineering Junior Faculty Teaching Excellence Award, the 2007 North American Molecular Beam Epitaxy Young Investigator Award, the 2007 National Consortium for Measures and Signatures Intelligence Research Defense Intelligence Agency (NCMR-DIA) Chief Scientist Award for Excellence, and the 2008 Early Career Achievement Award from the International Society for Optical Engineers (SPIE) and the IEEE Nanotechnology Council.