IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 6, JUNE 2010 959

Long-Wave InAs/GaSb Superlattice Detectors Basedon 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 cur-rent density and responsitivity of the pin photodetectors on dopingtype and level is investigated, and it is shown that dark currentdensity decreases while responsivity and detectivity increase byp-doping the absorbing region of pin detectors. Comparison ofoptical and electrical properties of SL photodetectors based on thenBn and pin designs is reported. nBn devices have higher specificdetectivity �� �, responsivity, and lower dark current densityas compared to the pin detectors. The decrease in dark currentin nBn devices is due to suppression of Shockley–Reed–Halland surface leakage currents. A specific detectivity �� � of7.15 10� cm Hz� � W � at 0.1 V, a responsivity of 1.28 A/Wand a quantum efficiency of 21.3% under 0.2 V biasing at 77 Kand 7 m, assuming unity gain, was obtained in the nBn device.

Index Terms—InAs/GaSb type-II superlattices, infrared detec-tors, longwave detector, nBn detector, pin detector.

I. INTRODUCTION

T HE InAs/GaSb type-II superlattice (SL) technology hasrecently shown significant development in infrared (IR)

technology and proven itself as a promising competitive tech-nology 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 thatthe effective bandgap of the SL can be tailored over a widerange m m by varying the thicknesses ofthe two “mid bandgap” constituent materials, namely GaSb andInAs. Moreover, the larger electron effective mass in these engi-neered one dimensional crystals helps to reduce tunneling cur-rents. Large splitting between heavy-hole and light-hole valencesubbands due to strain in the SLs contributes to the suppression

Manuscript received August 28, 2009; revised November 16, 2009, December23, 2009, and January 11, 2010. Current version published March 12, 2010. Thiswork is based on research supported by AFRL Contract FA9453-07-C-0171 andKRISS-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, De-partment of Electrical and Computer Engineering, University of NewMexico, Albuquerque, NM 87106 USA (e-mail: 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 andScience (KRISS), Daejeon 305-340, South Korea (e-mail: sjlee@kriss.re.kr;sknoh@kriss.re.kr).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JQE.2010.2041635

Fig. 1. Schematic of nBn design. Majority carriers (electrons) are blocked bythe barrier and minority carriers (holes) are the source of current.

of Auger recombination. SL based IR detectors have demon-strated high quantum efficiency [4], high temperature opera-tion [5], and are suitable for incorporation in focal plane arrays(FPA) by tapping into the mature III-V based growth and fabri-cation processes [6].

Most of the present day SL photodetectors are based on thepin photodiode design. In focal plane arrays based on pin diodes,pixels are separated from the their neighbor pixels by an etchedmesa. During the mesa isolation process, the periodic nature ofthe crystal structure ends abruptly at the mesa lateral surface.Disturbance of the periodic potential function due to a brokencrystal lattice leads to allowed electronic quantum states withinthe energy bandgap of SL resulting in large surface leakage cur-rents. The suppression of these currents by using a stable passi-vation layer for the etched mesa surface for the SL photodiodesis one of the primary limitations of the SL based technology. Aclass of IR detectors named nBn has shown promising results ineliminating the currents associated with Shockley–Read–Hall(SRH) centers and mesa lateral surface imperfections, whichhave resulted in an increase of the operating temperature [7] ascompared to the pin design. This so-called nBn structure con-sists of a n-type narrow bandgap contact and absorber layersseparated by a 50–100-nm-thick wide bandgap barrier layer. Aschematic of ideal nBn structure is shown in Fig. 1.

Implementation of the nBn design for InAs/GaSb midwaveinfrared (MWIR) SL single element and FPAs have been re-ported [3], [8], [9], but to date, little work has been reportedon the performance of long-wave infrared (LWIR) nBn baseddevices [10].

LWIR SL system is a residually n-type system due to thickerlayers of residually n-type InAs layers as compared to the resid-ually p-type GaSb layers. Therefore, the dopant material andits concentration is an important parameter in long-wave (LW)InAs/GaSb type-II SL design and growth, that can affect the op-tical and electrical properties of SLs structures. Beryllium (Be)doping the InAs layers has shown to be an effective method in

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960 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 6, JUNE 2010

decreasing the dark current by lowering the diffusion, genera-tion–recombination (GR) and tunneling currents and increasethe quantum efficiency of the device by switching to high mo-bility minority electron concentration [11].

In the present work, investigation of LWIR pin detector andthe influence of absorber p-doping on the optical and electricalproperties of the devices is presented. The optical and electricalproperties of LWIR nBn based detectors are also reported andcompared 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 alongthe [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 com-pressive (tensile) strain can build up inside SLs structure thataffects the structural, optical and electrical properties of the SLdramatically. Development of an optimized growth procedurefor the strain-balanced SL with well-ordered constituent andinterfacial layers is critical for the realization of a photodetectoroperating in the LWIR range (8–12 m) with large absorptioncoefficient and reduced dark current. For the purpose of strainoptimization in the LWIR SL structure, two sets of sampleswith 60 periods of SL with the same composition (13 MLsInAs/7 MLs GaSb) and different methods of InSb interfaceformation were investigated.

In the first method, an InSb layer was inserted between InAsand GaSb layers. In the second method, the insertion of an “InSblike” interface by using group V soak times was investigated.The insertion of an InSb layer in the SL structure resulted in thelowest full-width at half-maximum (FWHM) for the first ordersatellite peak and lowest lattice mismatch between the SL andthe GaSb substrate from XRD as compared to the structuresgrown with insertion of group V soak times. Detailed growthand interface optimization of LW SLs is not described here andcan be found elsewhere [12]. High resolution X-ray diffraction(HXRD) scan and cross-sectional scanning transmission elec-tron microscopy (STEM) of the grown structures are shown inFig. 2(a) and (b), respectively. X-ray diffraction rocking curvereveals intense satellite peaks attesting a good crystalline qualityof the layers and the zeroth-order SL peak position indicatesthat the SL is practically lattice matched to the GaSb substrate.STEM image also shows sharp and well defined interfaces forSL structure which is an indication of high quality growth.

To study the influence of p-doping of the absorbing regionof pin SL detectors on the device performance, a set of threepin detectors along with one nBn detector were grown. Toenable device comparisons, all four samples had exact samethicknesses for the absorbing region. Devices were grownon Te-doped epi-ready (100) GaSb substrates using a solidsource molecular beam epitaxy VG-80 system. The systemwas equipped with SUMO cells for gallium and indium, astandard effusion cell for aluminum and cracker cells for an-timony and arsenic. Detector based on nBn design consistedof 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 STEMimage of nBn detector. Top contact and active region are formed by 13 MLInAs/7GaSb SL, Al GaSb barrier and GaSb spacer are also shown.

region formed by 13 MLs InAs/0.75 ML InSb/7 MLs GaSbSL was grown followed by a 100-nm-thick Al GaSb bar-rier layer. The Al GaSb barrier layer was capped witha 20-nm-thick GaSb spacer to avoid oxidation of the Alduring the processing steps. The structure was terminatedby a 125-nm-thick n-type cm top con-tact layer with the same composition as the bottom con-tact layer. Detectors based on pin design consisted of a473 nm thick bottom contact layer formed by 13 MLs InAs:Si

cm 0.75 ML InSb 7 MLs GaSb SLfollowed by 250-nm-thick doping graded layers of 13 MLsInAs:Si/0.75 ML InSb/7 MLs GaSb SL to achieve dopingconcentration of cm before the absorbinglayer. Then a 1.9 m thick absorber formed by 13 MLsInAs/0.75 ML InSb/7 MLs GaSb SL was grown followedby 250-nm-thick p-doping graded layers. The structure wasterminated by a 125–nm-thick p-type cmtop contact layer with the same composition as the bottomcontact layer. The absorber region doping level was varied(Be-doped: cm , Be-doped: cm andundoped) during the growth of the three pin detectors. The

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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 struc-tures.

Fig. 4. Schematic of (a) conventionally defined mesa; (b) shallow etched iso-lation nBn device. In the latter case, the active area is defined by the diffusionlength (DL) of the minority carriers (holes).

heterostructure schematics of the pin and nBn structures arepresented in Fig. 3(a) and (b), respectively.

III. PROCESSING OF PIN AND NBN PHOTODETECTORS

The devices were processed using 410 410 m squaremesas with circle apertures with varying radii from 25 to300 m. Processing was initiated by standard optical pho-tolithography for top contact metal deposition. Then, a shallowisolation etch was undertaken using inductively coupled plasma(ICP) dry etch to the top of the barrier layer for the nBn struc-ture with an etch depth of 125 nm. Thus, the active absorberlayer underneath is not exposed. Then, ICP dry etch to themiddle of the bottom contact layer was performed for bothnBn and pin structures. SiN passivation was performed for pindetectors. Finally, samples were patterned and bottom contactmetal was deposited. Ti/Pt/Au (500/500/3000 ) were used ascontact metals for both top and bottom contacts. Schematics ofprocessed 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 bydimensions of etched but confined by a lateral diffusion lengthof minority carriers (holes), as illustrated in Fig. 4(b).

IV. CHARACTERIZATION

The bandgap of 60 periods of the 13 MLs of InAs and 7 MLsof GaSb SL material system was first determined through room

Fig. 5. (a) Absorbance as a function of wavelength. The cut-off wavelengthwas found to be � 8 �m (300 K). (b) Spectral response of nBn structure.

temperature absorption measurements, which were performedusing a Nicolet-870 Nexus Fourier transform infrared (FTIR)spectrometer and the reflectivity module associated with it. Thereflectance of the sample was calculated as ratio between the re-flected signals measured from the sample and a reference sub-strate (n-type GaSb). In order to eliminate the transmission com-ponent from the consideration, a thin layer of gold (50 nm thick)was deposited on the backside of both the sample and the refer-ence substrate. Thus, the absorbance ( ) as a function of wave-length is calculated using , where is the measuredtwo pass reflectance of the sample. The representative absorp-tion spectrum is shown in Fig. 5(a). The cut-off wavelength (de-fined as the wavelength where the response went to zero) wasfound to be 8 m (at 300 K).

Spectral measurements of the pin and nBn detectors wereperformed using a Nicolet 670 FTIR spectrometer and aKeithley 428 preamplifier. Relative spectral response was ob-tained by dividing the photocurrent of the SL detectors with thatobtained using a calibrated [13] deuterated triglycine sulfate(DTGS) thermal detector. The relative spectral response of nBnstructure as a function of wavelength is shown in Fig. 5(b).The spectral response of pin structure is similar to the nBndetector since both have the same absorbing region. The data

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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 biasin nBn design is defined where negative bias is applied on the top of device andreverse bias in pin design is defined where negative bias is applied on the top ofdevice.

clearly shows cutoff wavelength of 8 m and is in a goodagreement with the reflectivity measurements.

Current–voltage measurements were obtained using a semi-conductor parameter analyzer. Fig. 6 presents the dark currentdensity of pin and nBn structures at 77 K.

The data shows that the dark current density of the pin detec-tors decreases with p-doping the InAs layers in the absorbingregion. The lowest dark current density is associated with thesample which the Be doping concentration in InAs layers is

cm . In this comparison we neglect the effect ofsurface leakage currents since all three pin samples were iden-tically processed and passivated. The main dark current com-ponents in these detectors are diffusion, generation–recombina-tion and tunneling current. By increasing the doping level, dif-fusion current decreases. The generation–recombination currentalso decreases due to decrease in depletion width. Thus, totaldark current density associated with diffusion and generationrecombination decreases up to a certain doping concentration( cm Be doped) but as the doping concentration in-creases more, the maximum electric field across the depletionregion increases which causes the tunneling probability to in-crease. This can explain the larger dark current density for the

cm Be doped sample compared to the n.i.d sampleat bias points larger than 0.35 V. Detailed dark current mecha-nisms in the Be-doped pin detectors can be found in [11].

The optimized pin sample in terms of dark current densityis then compared with the nBn detector. Dark current densityin ( cm Be doped) pin structure is (0.08 A/cm at

100 mV) as compared to the nBn based design (0.05 A/cmat 100 mV). Dark current density measurements of the nBndesign were measured with a 300 K background while the pindark current density measurements are performed with a coldshield. Deeply etched nBn devices [14] also show lower darkcurrent density than the undoped pin devices. The lower darkcurrent density in deeply ethced nBn design is associated witha reduction of SRH centers due to smaller depletion region ascompared to undoped pin devices. Therefore, lower dark curentdensity of shallow etched nBn devices as compared to pin de-vices is attributed to reduction of both SRH centers and mesalatera surface imperfection. In order to completely eliminate the

dark current associated with SRH centers, an optimized barrierwith zero valence band offset is required. In the nBn structuresused for this study, the presence of small valence band discon-tinuity in the structure, results in formation of small depletionregion thus there is dark current component due to SRH centers.nBn structure, could also have lateral diffusion of minority car-riers (holes), which is ignored in this analysis [15].

Responsivity and specific detectivity were measured at77 K using a pour-fill dewar and a Micron M365 calibrated800 K blackbody source. No antireflection coating was appliedon the devices. As is shown in Fig. 7(a), the responsivity of pindetectors increases with cm Be doping of the pho-todiode absorbing region. Further increase in the doping con-centration cm leads to a drop in responsitivity ofpin photodiodes. To understand this behavior qualitatively, it’sworth noticing that the responsivity of a photodetector is thenumber of collected carriers per incident photon. Therefore, it isproportional to the ratio of photo-carriers leaving the absorbingregion and photo-carriers recombining within the absorbing re-gion. When the absorption region is Be doped, the minoritycarriers switch to high mobility electrons as compared to thenonintentionally doped sample where the minority carriers areholes. The rate that carriers leave the absorbing region is fasterin Be doped samples as compared to n.i.d sample. Therefore,the probability of carrier recombination decreases and leads tohigher responsivity. However, at higher Be doping concentra-tions cm , mobility of minority carriers decreasesdue to the increase in scattering from the dopants. Fig. 7(a) alsoshows that nBn device has a higher responsivity as comparedto the pin devices. Photodiodes based on nBn design eliminateSRH recombination centers associated with depletion regionswhich are the main source of recombination mechanisms in pinphotodiodes, and therefore, more carriers are extracted from theabsorbing region which increases the responsivity of these de-vices. It is worth mentioning that the responsivity of nBn devicescan be improved further with optimizing the barrier band offsetsand thickness of these structures.

The shot-noise limited spectral detectivity of the devicewas estimated using

(1)

where is the responsivity, is the electronic charge, is thetemperature of the device, is Boltzmann’s constant, is thecurrent density, is the dynamic resistance, and is thediode area. Detectivity measurements for pin and nBn devicesare shown in Fig. 7(b). At 77 K, the measurements show thatthe nBn device has the highest detectivity as compared to thepin devices. The behavior seen in Fig. 7(b) for detectivties ofpin and nBn devices is well expected since it is a measure ofsignal (responsivity) to noise (dark current) ratio. Table I showssummarized values of dark current, responsivity and detectivityof pin and nBn devices.

V. SUMMARY AND CONCLUSION

The development of nBn and pin based detectors for theLWIR spectral regions using type-II InAs/GaSb SL was pre-sented. To have a precise comparison, all structures were grown

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KHOSHAKHLAGH et al.: LONG-WAVE InAs/GaSb SUPERLATTICE DETECTORS BASED ON nBn AND PIN DESIGNS 963

Fig. 7. (a) Responsivity and (b) detectivity measurements of the pin and nBndevices at 77 K; nBn structure has the highest responsivity and detectivity valuesas compared to pin structures.

TABLE ISUMMARY 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 re-gion. It was shown that by p-doping the absorbing region of thepin devices, dark current of the pin photodiodes decreases andthe pin responsivity and detectivity increases. Devices basedon the nBn design showed higher detectivity and responsivityvalues as compared to pin devices. These improvements indevice characteristics of nBn design as compared to pin designis attributed to reduction of dark current due to suppressionof currents associated with SRH centers and surface leakagecurrents.

REFERENCES

[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 super-lattice photodiode with cutoff of 12 �m,” Appl. Phys. Lett., vol. 90, no.23, p. 231108, 2007.

[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 photo-diodes in the midwavelength infrared range,” Appl. Phys. Lett., vol. 86,no. 23, p. 233106, 2005.

[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 bandresponse from InAs/Ga(In)Sb type II strain layer superlattice detec-tors,” Appl. Phys. Lett., vol. 91, no. 26, p. 263504, 2007.

[4] R. Rehm, M. Walther, J. Schmitz, J. Fleissner, F. Fuchs, J. Ziegler, andW. 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. 595707.

[5] E. Plis, S. J. Lee, Z. Zhu, A. Amtout, and S. Krishna, “InAs/GaSb su-perlattice detectors operating at room temperature,” , IEEE J. Sel. Top.Quantum Electron., vol. 12, no. 6, pp. 1269–1274, Nov.–Dec. 2006.

[6] P.-Y. Delaunay, B. M. Nguyen, D. Hoffman, and M. Razeghi, “High-performance focal plane array based on InAs-GaSb superlattices witha 10-�m cutoff wavelength,” , IEEE J. Quantum Electron., vol. 44, no.5, pp. 462–467, May 2008.

[7] S. Maimon and G. W. Wicks, “nBn detector, an infrared detector withreduced dark current and higher operating temperature,” Appl. Phys.Lett., vol. 89, no. 15, p. 151109, 2006.

[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-IIstrained layer superlattices,” Appl. Phys. Lett., vol. 91, no. 4, p. 043514,2007.

[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 arraybased on type-II InAs/GaSb strain layer superlattice detector with nBndesign,” Appl. Phys. Lett., vol. 92, no. 18, p. 183502, 2008.

[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 wavelengthsuperlattice complementary barrier infrared detector,” Appl. Phys.Lett., vol. 95, no. 2, p. 023508, 2009.

[11] D. Hoffman, B.-M. Nguyen, P.-Y. Delaunay, A. Hood, M. Razeghi, andJ. Pellegrino, “Beryllium compensation doping of InAs/GaSb infraredsuperlattice photodiodes,” Appl. Phys. Lett., vol. 91, no. 14, p. 143507,2007.

[12] A. Khoshakhlagh, E. Plis, S. Myers, Y. Sharma, L. Dawson, and S.Krishna, “Optimization of InAs/GaSb type-II superlattice interfaces forlong-wave (8 �m) infrared detection,” J. Crystal Growth, vol. 311, no.7, pp. 1901–1904, 2009, International Conference on Molecular BeamEpitaxy (MBE-XV), The 15th International Conference on MolecularBeam Epitaxy (MBE-XV).

[13] J. W. Little, S. P. Svensson, W. A. Beck, A. C. Goldberg, S. W. Ken-nerly, T. Hongsmatip, M. Winn, and P. Uppal, “Thin active region, typeII superlattice photodiode arrays: Single-pixel and focal plane arraycharacterization,” J. Appl. Phys., vol. 101, no. 4, p. 044514, 2007.

[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-iistrain layer superlattice,” J. Vacuum Science and Technology B, vol.26, no. 3, pp. 1145–1148, 2008.

[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/GaSbstrained layer superlattice detectors,” Appl. Phys. Lett., vol. 93, no. 12,p. 123507, 2008.

Arezou Khoshakhlagh received the B.S. degree(with honors) and M.S. degree in electrical engi-neering, in 2004 and 2008 from the University ofNew Mexico, Albuquerque, where she is currentlyworking toward the Ph.D. degree in optical sciencesand engineering. She also has a Ph.D. minor innano-technology and microsystems from the Uni-versity of New Mexico.

Her research interests include design, molecularbeam 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 spon-sored NSMS-IGERT program.

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964 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 46, NO. 6, JUNE 2010

Stephen Myers received the B.S degree in engi-neering physics in May 2007 from Tarleton StateUniversity, Texas A&M. He was then acceptedinto the Nanoscience and Microsystems IntegrativeGraduate Education and Research Traineeship(NSMS IGERT) fellowship at the University ofNew Mexico, where he is presently working withProf. Sanjay Krishna. He is currently working ondeveloping infrared detector based on type-II strainlayered superlattices.

HaSul Kim is currently pursuing the Ph.D. degree inoptical science and engineering at the University ofNew Mexico. He was at the University of Alabama,Huntsville, and at Brigham Young University prior tojoining UNM. He also has extensive industrial expe-rience that he is tapping into as he investigates novelstrategies to realize high performance focal plane ar-rays based on strained layer superlattices.

Elena Plis received the Engineering degree fromthe Kovrov State Technological Academy, Russia,in 2001, the M.S. degree in electrical engineering in2005 and the Ph.D. degree in electrical engineeringin 2007 from the University of New Mexico.

She is an Assistant Research Professor at theCenter for High Technology Materials at the Univer-sity of New Mexico. Her present research interestsinclude growth, fabrication and characterization oftype-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 andapplication of IR sensors for early skin cancer detection.

Nutan Gautam received the B.Sc. (Hons.) inphysics and the M.Sc. in physics from DayalbaghEducational Institute, Agra, India, in 2003 and 2005,respectively, and the M.Tech. (EE/photonics) fromthe Indian Institute of Technology, Kanpur, India, inJuly 2007.

She worked as a scientist in Bhabha AtomicResearch Centre, Mumbai, India, from August2007 to July 2008. She joined the Electrical En-gineering Department, University of New Mexico,as a graduate student in Fall 2008. Since then, she

has been working with Prof. Krishna towards the Ph.D. degree. Her researchinterests are nanostructure semiconductor device modeling, growth and opticalcharacterization.

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 theCenter for Electro-Optics, Korea Advanced Instituteof Science and Technology, Daejeon. In 2002, Hejoined the Korea Research Institute of Standards andScience at Daejeon, where he is currently a SeniorResearch Scientist in at the Center for AdvancedMeasurement and Instrumentation. In 2005–2006and 2008, he worked as the visiting scientist of

the Prof. S. Krishna group at University of New Mexico, Albuquerque. Hisresearch interests include the epitaxial growth of the self-assembled quantumdots (SAQD) and type II strained layer superlattices (SLS) with MBE, fabrica-tion of infrared focal plane array using SAQD and SLS structures and hybridbonding technology.

Sam Kyo Noh received the M.Sc. and Ph.D. degreesfrom Yonsei University, Seoul, Korea, in 1980 and1986, respectively, both in semiconductor physics.

He was a Postdoctoral Researcher at BrownUniversity, Providence, RI, and the Frontier Re-search Laboratory of RIKEN, Wako, Japan, during1987–1989. In 1989, he joined Korea ResearchInstitute of Standards and Science (KRISS), Dae-jeon, Korea, as a Group Leader, and is currentlya Principal Research Scientist. He was a VisitingResearcher at Electrical and Computer Engineering

Department, University of Michigan, Ann Arbor, in 2000, and the Universityof California at Los Angeles in 2007. He is also a PI of the Global ResearchLaboratory (GRL) on Quantum Detector Technology, which collaborates withthe University of New Mexico, Albuquerque. His current research interestsinclude growth and fabrication of nanoscale structures and devices, especiallyfor quantum-dot and superlattice-based far-infrared/terahertz detectors. He hasauthored or coauthored and presented more than 100 research papers each injournals and conferences.

Dr. Noh was awarded the Presidential Medal of Merit (Korean Government)in 2003 and the Academic Achievement Prize (Korean Physical Society) in 2004in recognition of works on quantum semiconductors.

L. Ralph Dawson received the B.S. degree inelectrical engineering from the California Institute ofTechnology, Pasadena, the M.S. and Ph.D. degreesin electrical engineering from the University ofSouthern California, Los Angeles.

He is a Research Professor in the EECE De-partment, Center for High Technology Materials,University of New Mexico, Albuquerque. He was aDistinguished Member of Technical Staff at SandiaNational Laboratories, Albuquerque, and formerlya Member of Technical Staff, Bell Laboratories,

Murray Hill, NJ, from 1969 to 1976. His research interests are MBE growthof III-V arsenides and antimonides for IR emitters and detectors, monolithicintegration of Silicon and III-V device structures, and MBE growth of highlymismatched materials. He has more 185 journal publications, 160 conferencepresentations, and 12 patents. He is also editor of six proceedings volumes.

Sanjay Krishna (SM’08) received the Master’sdegree in physics from the Indian Institute of Tech-nology (IIT) Madras, Chennai, India, in 1996, andthe M.S. degree in electrical engineering and thePh.D. degree in applied physics from the Universityof Michigan, Ann Arbor, in 1999 and 2001, respec-tively.

In 2001, he joined the University of New Mexico,Albuquerque, as a Tenure Track Faculty Member andis currently an Associate Professor of electrical andcomputer engineering at the Center for High Tech-

nology Materials. His current research interests include growth, fabrication, andcharacterization of self-assembled quantum dots and type II InAs/InGaSb-basedstrain layer superlattices for midinfrared detectors. He has authored or coau-thored more than 70 peer-reviewed journal articles, more than 40 conferencepresentations, two book chapters, and holds two issued and five pending patents.

Dr. Krishna received the Gold Medal from the IIT Madras in 1996. Hereceived the Best Student Paper Award at the 16th North American Conferenceon Molecular Beam Epitaxy (NAMBE), Banff, AB, Canada, in 1999, the 2002Ralph E. Powe Junior Faculty Award from Oak Ridge Associated Universi-ties, the 2003 IEEE Outstanding Engineering Award, the 2004 OutstandingResearcher 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 IntelligenceResearch–Defense Intelligence Agency (NCMR-DIA) Chief Scientist Awardfor Excellence, and the 2008 Early Career Achievement Award from the Inter-national Society for Optical Engineers (SPIE) and the IEEE NanotechnologyCouncil.

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