We report on the comparison of mesa sidewall profiles of InAs/GaSb strainedlayer superlattice (SL... more We report on the comparison of mesa sidewall profiles of InAs/GaSb strainedlayer superlattice (SLS) detector structures (k 50% cutoff % 14 lm at V bias = 0 V and T = 30 K) obtained after (a) a conventional BCl 3-based inductively coupled plasma etch, (b) a chemical etch (H 2 O 2 :HCl:H 2 O, 1:1:4), and (c) a combination of both etches. We found that the smoothest sidewall profile with reasonable undercut ($5 lm) was obtained after chemical etch only. The chemical etch was optimized primarily using an n-type GaSb substrate. During this process, numerous chemical etchants were examined. GaSb n-type substrates were chosen for this study in preference over InAs substrates due to their high chemical reactivity and the complicated composition of the native oxide. In addition, SLS detectors are usually grown on GaSb substrates and, after hybridization of the focal-plane array to the readout integrated circuit, the GaSb substrate is etched away using a combination of wet and dry etching techniques. We found that H 2 O 2 :HCl:H 2 O (1:1:4) etching solution provided the smoothest etched surface of GaSb, with a root-meansquare roughness of 1.59 nm.
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2010
The authors report the InAs/InGaAs/GaAs/AlGaAs quantum dots-in-double-well ͑D-DWELL͒ design, whic... more The authors report the InAs/InGaAs/GaAs/AlGaAs quantum dots-in-double-well ͑D-DWELL͒ design, which has a lower strain per DWELL stack than the InAs/InGaAs/GaAs DWELLs thereby enabling the growth of many more stacks in the detector. The purpose of this study is to examine the effects of varying the number of stacks in the double DWELL detector on its device performance. The structures are grown by solid source molecular beam epitaxy on GaAs substrates. After fabrication of single pixel devices, a series of device measurements such as spectral response, dark current, total current, and responsivity were undertaken and the photoconductive gain and the activation energies were extracted. The goal of these experiments is not only to optimize the device performance by optimizing the number of stacks but also to investigate the transport properties as a function of the number of stacks.
The temperature-dependent behaviour of the bandgap of mid- and long-wavelength as well as dual-co... more The temperature-dependent behaviour of the bandgap of mid- and long-wavelength as well as dual-colour (mid-/long-wavelength) infrared detectors based on InAs/GaSb strained layer superlattices (SLSs) with p-i-n and nBn designs has been investigated with temperature-dependent absorption, photoluminescence and spectral response techniques. Values of Varshni parameters, zero temperature bandgap E0 and empirical coefficient alpha, were extracted and tabulated. The MWIR and LWIR superlattice detectors showed a temperature change of 0.325 meV K-1 and 0.282 meV K-1, respectively. These values are a factor of two lower than that of HgCdTe and InSb, making them attractive for higher operating temperatures.
Infrared (IR) detectors today are being utilized for a variety of imaging applications such as me... more Infrared (IR) detectors today are being utilized for a variety of imaging applications such as medical diagnostics, navigation instruments of automobiles and aircrafts, meteorological imaging, night-vision and fog/smoke imaging, surveillance, target acquisition and astronomical/space imaging. These wide ranging implementations have given rise to varied design requirements for these devices such as the required sensitivity, operating temperature, spectral sensitivity, peak wavelength and cost. Type-II band aligned InAs/Ga(In)Sb strained layer superlattice (SLS) material system proposed for the IR detection in the 1970s has been considered in recent years as an interesting alternative to the present day IR detection technologies. Type-II SLS technology posses mature growth technologies ix able to achieve uniformity over large areas along with band-gap tunability which results in IR detectors in mid wave (MW), long-wave (LW) and very long-wave infrared (VLWIR) ranges. The large electron effective mass in SLS help in reducing inter-band tunneling and hence allow for longer-wavelength operation in these IR detectors. Large splitting between heavy-hole and light-hole valence subbands due to strain in the SLSs contributes to the suppression of Auger recombination and this enables significantly higher operating temperatures. The commercialization of type-II SLS technology has been hindered by material defects that promote excess dark currents in the bulk and on detector surfaces. During SLS device fabrication the mesa delineation leads to discontinuity of the periodic crystal structure which results in formation of unsatisfied chemical bonds on the etched surfaces and hence enhancing the surface leakage currents. More-over, with the scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels surface to volume ratio. Hence the reduction of surface leakage currents in LWIR detectors has become a technological necessity and is the objective of this dissertation. This work focuses on performance improvement of InAs/GaSb SLS LWIR detectors by optimization of mesa delineation and surface passivation techniques. The first part of the dissertation works on the development of optimized etching scheme for the 400µm x 400µm area single-pixel SLS detectors and for 25µm x 25µm area focal plane arrays (FPAs). Firstly, optimization of wet chemical etches were carried out on GaSb substrates and reported here is that HCl:H 2 O 2 :H 2 O (1:1:4) solution rendered the smoothest etched surface with a root mean square (RMS) roughness of 1.59nm. This work also reports the results of comparison of mesa sidewall profiles of InAs/GaSb SLS single-pixel and FPA detectors obtained after (a) a conventional BCl 3 gas based inductively coupled plasma dry etch, (b) a HCl:H 2 O 2 :H 2 O (1:1:4) solution wet chemical etch and (c) combination of both. It was found that HCl:H 2 O 2 :H 2 O (1:1:4) solution wet etch was ideal for single pixel x mesa delineation, but not on FPA device proportions. In the etch study experiments, the InAs/GaSb SLS structure was looked at as one single entity and as an amalgamation of its constituents InAs and GaSb materials. The second part of this research deals with the development of efficient surface passivation methods for the long wave infrared (LWIR) SLS detectors with pin, pBiBn, and graded bandgap designs. A comparative study of dielectric passivants (Silicon di-oxide and Silicon nitride) versus organic passivant of SU-8 versus chalcogenide passivants (Zinc Sulfide, Ammonium Sulfide and Electro-chemical passivation i.e. deposition of pure sulphur) were carried out on InAs/GaSb SLS LWIR single-pixel detectors. Ammonium sulfide [(NH 4 ) 2 S] treatment and electrochemical sulfur deposition (ECP) reduced dark current density (J d ) at 77K and applied bias= -0.1V by (a) by factor of 25 and 200 in InAs/GaSb SLS LWIR detector with p-i-n design and (b) by factor of 3 and 54 in InAs/GaSb SLS LWIR with pBiBn design. In the comparative study of all the sulphur-based passivants of thioacetamide (acid-based and base-based), (NH 4 ) 2 S and ECP on graded-bandgap design based single-pixel LWIR SLS detectors, ECP showed superior performance of all with the highest surface resistivity (r sur f ace ) of 1.4x10 5 Ω-cm at 77K. In the long term stability study of ECP, it showed degradation over time with J d =0.09A/cm 2 right after passivation and J d =2.18A/cm 2 after 4 weeks of passivation. Hence as an alternative to ECP (i.e. sulphur passivation), we propose the utilization of novel chlorine-doped Zinc Telluride (ZnTe:Cl) as a passivation technique. It is for the first time that ZnTe:Cl has been used as a passivation technique on any IR device. This novel ZnTe:Cl passivation technique is implemented on InAs/GaSb SLS LWIR single-pixel detectors with pin and graded-bandgap designs. Though ECP showed a superior r sur f ace =10 5 Ω-cm over ZnTe:Cl passivation with rsurface =6700Ω-cm, ZnTe:Cl passivation had almost no degradation over time. Hence an improved ZnTe:Cl with its robust, uniform passivation layer has the potential to replace ECP in FPA fabrication on InAs/GaSb SLS LWIR detectors and there-of xi take these high-performing SLS-based IR detectors to commercialization.
Relationship between V/III beam equivalent pressure (BEP) flux ratios during the molecular beam e... more Relationship between V/III beam equivalent pressure (BEP) flux ratios during the molecular beam epitaxial (MBE) growth of long-wave infrared InAs/GaSb strained layer superlattice (SLS) material, crystalline quality of asgrown material, and devices' signal (responsivity) and noise (dark current) characteristics was investigated. It was found that the V/III ratio is a critical factor affecting the dark current, cut off wavelength and
InAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were... more InAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were first proposed as an infrared (IR) sensing material more than three decades ago. The basic material properties of SLS provide a prospective benefit in the realization of IR imagers with suppressed interband tunneling and Auger recombination processes, as well as high quantum efficiency and responsivity. With scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels' surface/volume ratio. This article discusses the cause of surface leakage currents and various approaches of their reduction including dielectric passivation, passivation with organic materials (polyimide or various photoresists), passivation by overgrowth of wider bandgap material, and chalcogenide passivation. Performance of SLS detectors passivated by different techniques and operating in various regions of infrared spectrum has been compared.
ABSTRACT The development of InAsSb detectors based on the nBn design for the mid-wave infrared (M... more ABSTRACT The development of InAsSb detectors based on the nBn design for the mid-wave infrared (MWIR) spectral region is discussed. Comparisons of optical and electrical properties of InAsSb photodetectors with two different barrier material, namely, AlAs 0.15Sb0.75 (structure A) and AlAs0.10Sb0.9 (structure B) are reported. The dark current density in the AlAs0.15Sb0.85 is lower possibly due to the larger valence band offset. Clear room temperature spectral responses is observed and a specific detectivity (D*) of 1.4x1012 and 1.01x1012 cmHz1/2/W at 0.2 V, and a responsivity of 0.87 and 1.66 A/W under 0.2 V biasing at 77 K and 3.5 mum, assuming unity gain, was obtained for structures A and B, respectively.
Background: Pregabalin, a γ-amino-n-butyric acid derivative, is an antiepileptic drug not yet off... more Background: Pregabalin, a γ-amino-n-butyric acid derivative, is an antiepileptic drug not yet official in any pharmacopeia and development of analytical procedures for this drug in bulk/formulation forms is a necessity. We herein, report a new, simple, extraction free, cost effective, sensitive and reproducible spectrophotometric method for the determination of the pregabalin. Results: Pregabalin, as a primary amine was reacted with ninhydrin in phosphate buffer pH 7.4 to form blue violet colored chromogen which could be measured spectrophotometrically at λ max 402.6 nm. The method was validated with respect to linearity, accuracy, precision and robustness. The method showed linearity in a wide concentration range of 50-1000 μg mL-1 with good correlation coefficient (0.992). The limits of assays detection was found to be 6.0 μg mL-1 and quantitation limit was 20.0 μg mL-1. The suggested method was applied to the determination of the drug in capsules. No interference could be observed from the additives in the capsules. The percentage recovery was found to be 100.43 ± 1.24. Conclusion: The developed method was successfully validated and applied to the determination of pregabalin in bulk and pharmaceutical formulations without any interference from common excipients. Hence, this method can be potentially useful for routine laboratory analysis of pregabalin.
Our group is investigating nBn detectors based on bulk InAs(1-x)Sb(x) absorber (n) and contacts (... more Our group is investigating nBn detectors based on bulk InAs(1-x)Sb(x) absorber (n) and contacts (n) with an AlAs(1-x)Sb(x) barrier (B). The wide-band-gap barrier material exhibits a large conduction band offset and small valence band offset with respect to the narrow-band-gap absorber material. An important matter to explore in this design is the barrier parameters (material, composition and doping concentration) and
ABSTRACT We present our efforts on development of high performance low noise, long-wave infrared ... more ABSTRACT We present our efforts on development of high performance low noise, long-wave infrared (LWIR) and multicolor detectors based on the InAs/GaSb strained layer material (SLS) material system. The LWIR SLS detector with PbIbN architecture showed improved performance over the conventional PIN design due to unipolar current blocking layers. At 77K and Vb=-0.25V, a responsivity of 1.8 A/W, dark current density of 1.2 mA/cm2, quantum efficiency of 23% and shot noise limited detectivity (D*) of 8.7×1010 Jones (lambdac = 10.8 mum) has been observed. Dual band response was registered with 50% cut-off wavelengths of 5mum and 10mum from an SLS detector with the pBp design. The responsivity equal to 1.6 A/W (at lambda = 5 mum and Vb = +0.4 V) and 1.8 A/W (at lambda = 9 mum and Vb = -0.7 V) for MWIR and LWIR absorbers was achieved with corresponding values of specific detectivity 5 x 1011 Jones and 2.6 x 1010 Jones, respectively. The maximum values of quantum efficiency were estimated to 41% (MWIR) and 25% (LWIR) at Vb = +0.4V and Vb = -0.7V. Moreover, the diffusion-limited behavior of dark current at higher temperatures was observed for the MWIR absorber for pBp detector. Finally, three-color response was registered from three contact device with nBn architecture for SWIR and MWIR and heterojunction PIbN architecture for LWIR detection (NbNbiP). At 77K, the cut-off wavelength for SWIR, MWIR and LWIR regions have been observed as 3.0 mum, 4.7 mum, and 10.1 mum respectively. At the same temperature, D* of 1.4 × 1010 Jones, 1.8 × 1010 Jones and 1.5 × 109 Jones for SWIR, MWIR and LWIR signals has been observed.
2009 34th International Conference on Infrared, Millimeter, and Terahertz Waves, 2009
As infrared focal plane arrays (FPAs) have evolved from the first generation of linear arrays to ... more As infrared focal plane arrays (FPAs) have evolved from the first generation of linear arrays to the second generation of small format staring arrays to the present "third-gen" devices, there is an increased emphasis on large area focal plane arrays with multicolor operation and higher operating temperature. In this paper, we will discuss how one needs to develop an increased
... Nutan Gautam, Ajit V. Barve, Stephen Myers, Brianna Klein, , Elena Plis, Mikhail Naydenkov,Ma... more ... Nutan Gautam, Ajit V. Barve, Stephen Myers, Brianna Klein, , Elena Plis, Mikhail Naydenkov,Maya N. Kutty, Ted Schuler-Sandy and S. Krishna Center for High Technology Materials, Dept of Electrical and Computer Engineering, University of New Mexico ... [2] GA Sai-Halasz, R ...
Long-wave infrared (LWIR) detector technologies with the ability to operate at or near room tempe... more Long-wave infrared (LWIR) detector technologies with the ability to operate at or near room temperature are very important for many civil and military applications including chemical identification, surveillance, defense and medical diagnostics. Eliminating the need for cryogenics in a detector system can reduce cost, weight and power consumption; simplify the detection system design and allow for widespread usage. In recent years, infrared (IR) detectors based on uni-polar barrier designs have gained interest for their ability to lower dark current and increase a detector's operating temperature. Our group is currently investigating nBn and pBp detectors with InAs/GaSb strain layer superlattice (SLS) absorbers (n) and contacts (n), and AlGaSb and InAs/AlSb superlattice electron and hole barriers (B) respectively. For the case of the nBn structure, the wide-band-gap barrier material (AlGaSb) exhibits a large conduction band offset and a small valence band offset with the narrow-band-gap absorber material. For the pBp structure (InAs/AlSb superlattice barrier), the converse is true with a large valence band offset between the barrier and absorber and a small or zero conduction band offset. Like the built-in barrier in a p-n junction, the heterojunction barrier blocks the majority carriers allowing free movement of photogenerated minority carriers. However, the barrier in an nBn or pBp detector, in contrast with a p-n junction depletion layer, does not contribute to generation-recombination (G-R) current. In this report we aim to investigate and contrast the performance characteristics of an SLS nBn detector with that of and SLS pBp detector.
The device fabrication and integration of nanopatterned quantum dots (PQDs) are realized through ... more The device fabrication and integration of nanopatterned quantum dots (PQDs) are realized through the demonstration of a broad-area light-emitting diode with PQD active region. The device involves two growth processes, first to form PQDs by selective-area epitaxy on an SiO(2) mask and then to complete the device structure after mask removal. Linear current-voltage characteristics are observed with sharp turn-on, low leakage current and low forward resistance. Electroluminescence spectra show PQD intraband structure and low quenching of emission from 77 K to room temperature. Light-current measurements demonstrate external quantum efficiency per PQD comparable to self-assembled QDs, thus providing a possible route toward individually addressable single QD devices.
ABSTRACT We report a heterostructure bandgap engineered strained layer superlattice photodetector... more ABSTRACT We report a heterostructure bandgap engineered strained layer superlattice photodetector design for performance improvement for longwave infrared (LWIR) detection. At 77K, the dark current density of the reported device was at least two orders of magnitude lower than that of the conventional PIN superlattice photodiode. We have obtained a shot-noise limited detectivity of 8.7×1010cmHz1/2W−1 (λc=10.8μm), responsivity of 1.8A/W, 23% QE at 250mV of applied reverse bias. A three contact heterojunction bandgap engineered dual color detector was demonstrated with simultaneous detection of midwave and longwave infrared radiation. The design showed midwave responsivity of 0.93A/W and detectivity of 1.0×1011cmHz1/2W−1 (at 4μm) at 77K for Vb=−70mV. Longwave responsivity and detectivity of 1.5A/W and 2.42×1010cmHz1/2W−1 (at 10μm) were observed at −100mV of applied bias at 77K.
We report on effective sulfur-based passivation treatments of type-II InAs/GaSb strained layer su... more We report on effective sulfur-based passivation treatments of type-II InAs/GaSb strained layer superlattice detectors (100% cutoff wavelength is 9.8 lm at 77 K). The electrical behavior of detectors passivated by electrochemical sulfur deposition (ECP) and thioacetamide (TAM) was evaluated for devices of various sizes. ECP passivated detectors with a perimeter-to-area ratio of 1600 cm À1 exhibited superior performance with surface resistivity in excess of 10 4 X cm, dark current density of 2.7 Â 10 À3 A/cm 2 , and specific detectivity improved by a factor of 5 compared to unpassivated devices (V Bias = À 0.1 V, 77 K).
We report on the comparison of mesa sidewall profiles of InAs/GaSb strainedlayer superlattice (SL... more We report on the comparison of mesa sidewall profiles of InAs/GaSb strainedlayer superlattice (SLS) detector structures (k 50% cutoff % 14 lm at V bias = 0 V and T = 30 K) obtained after (a) a conventional BCl 3-based inductively coupled plasma etch, (b) a chemical etch (H 2 O 2 :HCl:H 2 O, 1:1:4), and (c) a combination of both etches. We found that the smoothest sidewall profile with reasonable undercut ($5 lm) was obtained after chemical etch only. The chemical etch was optimized primarily using an n-type GaSb substrate. During this process, numerous chemical etchants were examined. GaSb n-type substrates were chosen for this study in preference over InAs substrates due to their high chemical reactivity and the complicated composition of the native oxide. In addition, SLS detectors are usually grown on GaSb substrates and, after hybridization of the focal-plane array to the readout integrated circuit, the GaSb substrate is etched away using a combination of wet and dry etching techniques. We found that H 2 O 2 :HCl:H 2 O (1:1:4) etching solution provided the smoothest etched surface of GaSb, with a root-meansquare roughness of 1.59 nm.
Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, 2010
The authors report the InAs/InGaAs/GaAs/AlGaAs quantum dots-in-double-well ͑D-DWELL͒ design, whic... more The authors report the InAs/InGaAs/GaAs/AlGaAs quantum dots-in-double-well ͑D-DWELL͒ design, which has a lower strain per DWELL stack than the InAs/InGaAs/GaAs DWELLs thereby enabling the growth of many more stacks in the detector. The purpose of this study is to examine the effects of varying the number of stacks in the double DWELL detector on its device performance. The structures are grown by solid source molecular beam epitaxy on GaAs substrates. After fabrication of single pixel devices, a series of device measurements such as spectral response, dark current, total current, and responsivity were undertaken and the photoconductive gain and the activation energies were extracted. The goal of these experiments is not only to optimize the device performance by optimizing the number of stacks but also to investigate the transport properties as a function of the number of stacks.
The temperature-dependent behaviour of the bandgap of mid- and long-wavelength as well as dual-co... more The temperature-dependent behaviour of the bandgap of mid- and long-wavelength as well as dual-colour (mid-/long-wavelength) infrared detectors based on InAs/GaSb strained layer superlattices (SLSs) with p-i-n and nBn designs has been investigated with temperature-dependent absorption, photoluminescence and spectral response techniques. Values of Varshni parameters, zero temperature bandgap E0 and empirical coefficient alpha, were extracted and tabulated. The MWIR and LWIR superlattice detectors showed a temperature change of 0.325 meV K-1 and 0.282 meV K-1, respectively. These values are a factor of two lower than that of HgCdTe and InSb, making them attractive for higher operating temperatures.
Infrared (IR) detectors today are being utilized for a variety of imaging applications such as me... more Infrared (IR) detectors today are being utilized for a variety of imaging applications such as medical diagnostics, navigation instruments of automobiles and aircrafts, meteorological imaging, night-vision and fog/smoke imaging, surveillance, target acquisition and astronomical/space imaging. These wide ranging implementations have given rise to varied design requirements for these devices such as the required sensitivity, operating temperature, spectral sensitivity, peak wavelength and cost. Type-II band aligned InAs/Ga(In)Sb strained layer superlattice (SLS) material system proposed for the IR detection in the 1970s has been considered in recent years as an interesting alternative to the present day IR detection technologies. Type-II SLS technology posses mature growth technologies ix able to achieve uniformity over large areas along with band-gap tunability which results in IR detectors in mid wave (MW), long-wave (LW) and very long-wave infrared (VLWIR) ranges. The large electron effective mass in SLS help in reducing inter-band tunneling and hence allow for longer-wavelength operation in these IR detectors. Large splitting between heavy-hole and light-hole valence subbands due to strain in the SLSs contributes to the suppression of Auger recombination and this enables significantly higher operating temperatures. The commercialization of type-II SLS technology has been hindered by material defects that promote excess dark currents in the bulk and on detector surfaces. During SLS device fabrication the mesa delineation leads to discontinuity of the periodic crystal structure which results in formation of unsatisfied chemical bonds on the etched surfaces and hence enhancing the surface leakage currents. More-over, with the scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels surface to volume ratio. Hence the reduction of surface leakage currents in LWIR detectors has become a technological necessity and is the objective of this dissertation. This work focuses on performance improvement of InAs/GaSb SLS LWIR detectors by optimization of mesa delineation and surface passivation techniques. The first part of the dissertation works on the development of optimized etching scheme for the 400µm x 400µm area single-pixel SLS detectors and for 25µm x 25µm area focal plane arrays (FPAs). Firstly, optimization of wet chemical etches were carried out on GaSb substrates and reported here is that HCl:H 2 O 2 :H 2 O (1:1:4) solution rendered the smoothest etched surface with a root mean square (RMS) roughness of 1.59nm. This work also reports the results of comparison of mesa sidewall profiles of InAs/GaSb SLS single-pixel and FPA detectors obtained after (a) a conventional BCl 3 gas based inductively coupled plasma dry etch, (b) a HCl:H 2 O 2 :H 2 O (1:1:4) solution wet chemical etch and (c) combination of both. It was found that HCl:H 2 O 2 :H 2 O (1:1:4) solution wet etch was ideal for single pixel x mesa delineation, but not on FPA device proportions. In the etch study experiments, the InAs/GaSb SLS structure was looked at as one single entity and as an amalgamation of its constituents InAs and GaSb materials. The second part of this research deals with the development of efficient surface passivation methods for the long wave infrared (LWIR) SLS detectors with pin, pBiBn, and graded bandgap designs. A comparative study of dielectric passivants (Silicon di-oxide and Silicon nitride) versus organic passivant of SU-8 versus chalcogenide passivants (Zinc Sulfide, Ammonium Sulfide and Electro-chemical passivation i.e. deposition of pure sulphur) were carried out on InAs/GaSb SLS LWIR single-pixel detectors. Ammonium sulfide [(NH 4 ) 2 S] treatment and electrochemical sulfur deposition (ECP) reduced dark current density (J d ) at 77K and applied bias= -0.1V by (a) by factor of 25 and 200 in InAs/GaSb SLS LWIR detector with p-i-n design and (b) by factor of 3 and 54 in InAs/GaSb SLS LWIR with pBiBn design. In the comparative study of all the sulphur-based passivants of thioacetamide (acid-based and base-based), (NH 4 ) 2 S and ECP on graded-bandgap design based single-pixel LWIR SLS detectors, ECP showed superior performance of all with the highest surface resistivity (r sur f ace ) of 1.4x10 5 Ω-cm at 77K. In the long term stability study of ECP, it showed degradation over time with J d =0.09A/cm 2 right after passivation and J d =2.18A/cm 2 after 4 weeks of passivation. Hence as an alternative to ECP (i.e. sulphur passivation), we propose the utilization of novel chlorine-doped Zinc Telluride (ZnTe:Cl) as a passivation technique. It is for the first time that ZnTe:Cl has been used as a passivation technique on any IR device. This novel ZnTe:Cl passivation technique is implemented on InAs/GaSb SLS LWIR single-pixel detectors with pin and graded-bandgap designs. Though ECP showed a superior r sur f ace =10 5 Ω-cm over ZnTe:Cl passivation with rsurface =6700Ω-cm, ZnTe:Cl passivation had almost no degradation over time. Hence an improved ZnTe:Cl with its robust, uniform passivation layer has the potential to replace ECP in FPA fabrication on InAs/GaSb SLS LWIR detectors and there-of xi take these high-performing SLS-based IR detectors to commercialization.
Relationship between V/III beam equivalent pressure (BEP) flux ratios during the molecular beam e... more Relationship between V/III beam equivalent pressure (BEP) flux ratios during the molecular beam epitaxial (MBE) growth of long-wave infrared InAs/GaSb strained layer superlattice (SLS) material, crystalline quality of asgrown material, and devices' signal (responsivity) and noise (dark current) characteristics was investigated. It was found that the V/III ratio is a critical factor affecting the dark current, cut off wavelength and
InAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were... more InAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were first proposed as an infrared (IR) sensing material more than three decades ago. The basic material properties of SLS provide a prospective benefit in the realization of IR imagers with suppressed interband tunneling and Auger recombination processes, as well as high quantum efficiency and responsivity. With scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels' surface/volume ratio. This article discusses the cause of surface leakage currents and various approaches of their reduction including dielectric passivation, passivation with organic materials (polyimide or various photoresists), passivation by overgrowth of wider bandgap material, and chalcogenide passivation. Performance of SLS detectors passivated by different techniques and operating in various regions of infrared spectrum has been compared.
ABSTRACT The development of InAsSb detectors based on the nBn design for the mid-wave infrared (M... more ABSTRACT The development of InAsSb detectors based on the nBn design for the mid-wave infrared (MWIR) spectral region is discussed. Comparisons of optical and electrical properties of InAsSb photodetectors with two different barrier material, namely, AlAs 0.15Sb0.75 (structure A) and AlAs0.10Sb0.9 (structure B) are reported. The dark current density in the AlAs0.15Sb0.85 is lower possibly due to the larger valence band offset. Clear room temperature spectral responses is observed and a specific detectivity (D*) of 1.4x1012 and 1.01x1012 cmHz1/2/W at 0.2 V, and a responsivity of 0.87 and 1.66 A/W under 0.2 V biasing at 77 K and 3.5 mum, assuming unity gain, was obtained for structures A and B, respectively.
Background: Pregabalin, a γ-amino-n-butyric acid derivative, is an antiepileptic drug not yet off... more Background: Pregabalin, a γ-amino-n-butyric acid derivative, is an antiepileptic drug not yet official in any pharmacopeia and development of analytical procedures for this drug in bulk/formulation forms is a necessity. We herein, report a new, simple, extraction free, cost effective, sensitive and reproducible spectrophotometric method for the determination of the pregabalin. Results: Pregabalin, as a primary amine was reacted with ninhydrin in phosphate buffer pH 7.4 to form blue violet colored chromogen which could be measured spectrophotometrically at λ max 402.6 nm. The method was validated with respect to linearity, accuracy, precision and robustness. The method showed linearity in a wide concentration range of 50-1000 μg mL-1 with good correlation coefficient (0.992). The limits of assays detection was found to be 6.0 μg mL-1 and quantitation limit was 20.0 μg mL-1. The suggested method was applied to the determination of the drug in capsules. No interference could be observed from the additives in the capsules. The percentage recovery was found to be 100.43 ± 1.24. Conclusion: The developed method was successfully validated and applied to the determination of pregabalin in bulk and pharmaceutical formulations without any interference from common excipients. Hence, this method can be potentially useful for routine laboratory analysis of pregabalin.
Our group is investigating nBn detectors based on bulk InAs(1-x)Sb(x) absorber (n) and contacts (... more Our group is investigating nBn detectors based on bulk InAs(1-x)Sb(x) absorber (n) and contacts (n) with an AlAs(1-x)Sb(x) barrier (B). The wide-band-gap barrier material exhibits a large conduction band offset and small valence band offset with respect to the narrow-band-gap absorber material. An important matter to explore in this design is the barrier parameters (material, composition and doping concentration) and
ABSTRACT We present our efforts on development of high performance low noise, long-wave infrared ... more ABSTRACT We present our efforts on development of high performance low noise, long-wave infrared (LWIR) and multicolor detectors based on the InAs/GaSb strained layer material (SLS) material system. The LWIR SLS detector with PbIbN architecture showed improved performance over the conventional PIN design due to unipolar current blocking layers. At 77K and Vb=-0.25V, a responsivity of 1.8 A/W, dark current density of 1.2 mA/cm2, quantum efficiency of 23% and shot noise limited detectivity (D*) of 8.7×1010 Jones (lambdac = 10.8 mum) has been observed. Dual band response was registered with 50% cut-off wavelengths of 5mum and 10mum from an SLS detector with the pBp design. The responsivity equal to 1.6 A/W (at lambda = 5 mum and Vb = +0.4 V) and 1.8 A/W (at lambda = 9 mum and Vb = -0.7 V) for MWIR and LWIR absorbers was achieved with corresponding values of specific detectivity 5 x 1011 Jones and 2.6 x 1010 Jones, respectively. The maximum values of quantum efficiency were estimated to 41% (MWIR) and 25% (LWIR) at Vb = +0.4V and Vb = -0.7V. Moreover, the diffusion-limited behavior of dark current at higher temperatures was observed for the MWIR absorber for pBp detector. Finally, three-color response was registered from three contact device with nBn architecture for SWIR and MWIR and heterojunction PIbN architecture for LWIR detection (NbNbiP). At 77K, the cut-off wavelength for SWIR, MWIR and LWIR regions have been observed as 3.0 mum, 4.7 mum, and 10.1 mum respectively. At the same temperature, D* of 1.4 × 1010 Jones, 1.8 × 1010 Jones and 1.5 × 109 Jones for SWIR, MWIR and LWIR signals has been observed.
2009 34th International Conference on Infrared, Millimeter, and Terahertz Waves, 2009
As infrared focal plane arrays (FPAs) have evolved from the first generation of linear arrays to ... more As infrared focal plane arrays (FPAs) have evolved from the first generation of linear arrays to the second generation of small format staring arrays to the present "third-gen" devices, there is an increased emphasis on large area focal plane arrays with multicolor operation and higher operating temperature. In this paper, we will discuss how one needs to develop an increased
... Nutan Gautam, Ajit V. Barve, Stephen Myers, Brianna Klein, , Elena Plis, Mikhail Naydenkov,Ma... more ... Nutan Gautam, Ajit V. Barve, Stephen Myers, Brianna Klein, , Elena Plis, Mikhail Naydenkov,Maya N. Kutty, Ted Schuler-Sandy and S. Krishna Center for High Technology Materials, Dept of Electrical and Computer Engineering, University of New Mexico ... [2] GA Sai-Halasz, R ...
Long-wave infrared (LWIR) detector technologies with the ability to operate at or near room tempe... more Long-wave infrared (LWIR) detector technologies with the ability to operate at or near room temperature are very important for many civil and military applications including chemical identification, surveillance, defense and medical diagnostics. Eliminating the need for cryogenics in a detector system can reduce cost, weight and power consumption; simplify the detection system design and allow for widespread usage. In recent years, infrared (IR) detectors based on uni-polar barrier designs have gained interest for their ability to lower dark current and increase a detector's operating temperature. Our group is currently investigating nBn and pBp detectors with InAs/GaSb strain layer superlattice (SLS) absorbers (n) and contacts (n), and AlGaSb and InAs/AlSb superlattice electron and hole barriers (B) respectively. For the case of the nBn structure, the wide-band-gap barrier material (AlGaSb) exhibits a large conduction band offset and a small valence band offset with the narrow-band-gap absorber material. For the pBp structure (InAs/AlSb superlattice barrier), the converse is true with a large valence band offset between the barrier and absorber and a small or zero conduction band offset. Like the built-in barrier in a p-n junction, the heterojunction barrier blocks the majority carriers allowing free movement of photogenerated minority carriers. However, the barrier in an nBn or pBp detector, in contrast with a p-n junction depletion layer, does not contribute to generation-recombination (G-R) current. In this report we aim to investigate and contrast the performance characteristics of an SLS nBn detector with that of and SLS pBp detector.
The device fabrication and integration of nanopatterned quantum dots (PQDs) are realized through ... more The device fabrication and integration of nanopatterned quantum dots (PQDs) are realized through the demonstration of a broad-area light-emitting diode with PQD active region. The device involves two growth processes, first to form PQDs by selective-area epitaxy on an SiO(2) mask and then to complete the device structure after mask removal. Linear current-voltage characteristics are observed with sharp turn-on, low leakage current and low forward resistance. Electroluminescence spectra show PQD intraband structure and low quenching of emission from 77 K to room temperature. Light-current measurements demonstrate external quantum efficiency per PQD comparable to self-assembled QDs, thus providing a possible route toward individually addressable single QD devices.
ABSTRACT We report a heterostructure bandgap engineered strained layer superlattice photodetector... more ABSTRACT We report a heterostructure bandgap engineered strained layer superlattice photodetector design for performance improvement for longwave infrared (LWIR) detection. At 77K, the dark current density of the reported device was at least two orders of magnitude lower than that of the conventional PIN superlattice photodiode. We have obtained a shot-noise limited detectivity of 8.7×1010cmHz1/2W−1 (λc=10.8μm), responsivity of 1.8A/W, 23% QE at 250mV of applied reverse bias. A three contact heterojunction bandgap engineered dual color detector was demonstrated with simultaneous detection of midwave and longwave infrared radiation. The design showed midwave responsivity of 0.93A/W and detectivity of 1.0×1011cmHz1/2W−1 (at 4μm) at 77K for Vb=−70mV. Longwave responsivity and detectivity of 1.5A/W and 2.42×1010cmHz1/2W−1 (at 10μm) were observed at −100mV of applied bias at 77K.
We report on effective sulfur-based passivation treatments of type-II InAs/GaSb strained layer su... more We report on effective sulfur-based passivation treatments of type-II InAs/GaSb strained layer superlattice detectors (100% cutoff wavelength is 9.8 lm at 77 K). The electrical behavior of detectors passivated by electrochemical sulfur deposition (ECP) and thioacetamide (TAM) was evaluated for devices of various sizes. ECP passivated detectors with a perimeter-to-area ratio of 1600 cm À1 exhibited superior performance with surface resistivity in excess of 10 4 X cm, dark current density of 2.7 Â 10 À3 A/cm 2 , and specific detectivity improved by a factor of 5 compared to unpassivated devices (V Bias = À 0.1 V, 77 K).
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Papers by Maya Kutty