C. Grein - Academia.edu (original) (raw)
Papers by C. Grein
IGARSS 2023 - 2023 IEEE International Geoscience and Remote Sensing Symposium
Physical Review B, 2012
Employing ab initio thermodynamics calculations, we elucidate for the first time the effects of g... more Employing ab initio thermodynamics calculations, we elucidate for the first time the effects of growth conditions on the reconstruction phase diagram of the polar Cd-terminated CdTe (111) surface and resolve an existing experimental controversy of the low-temperature reconstruction under Te-rich conditions. We demonstrate that the Cd-vacancy (2 × 2) reconstruction is the most stable configuration in the allowed range of the Te chemical potential. Under Te-rich conditions, however, the calculations reveal a transition from a high-temperature semiconducting (2 × 2) to a low-temperature metallic (1 × 1)-Te n reconstruction consisting of n Te adlayers forming a spiral trigonal structure. We also predict the temperature and pressure dependence of the Te thickness adlayer, which has remained experimentally unresolved.
Applied Physics Letters
For short-wavelength infrared (SWIR) avalanche photodiodes, a separate absorption, charge, and mu... more For short-wavelength infrared (SWIR) avalanche photodiodes, a separate absorption, charge, and multiplication design is widely used. AlInAsSb on an InP substrate is a potential multiplication layer with a lattice match to absorber candidates across the SWIR. Our new measurements demonstrate that AlInAsSb on InP is a promising multiplier candidate with a relatively low dark current density of 10−4 A/cm2 at a gain of 30; a high gain, measured up to 245 in this study; and a large differentiation of electron and hole ionization leading to a low excess noise, measured to be 2.5 at a gain of 30. These characteristics are all improvements over commercially available SWIR detectors incorporating InAlAs or InP as the multiplier. We measured and analyzed gain for multiple wavelengths to extract the ionization coefficients as a function of an electric field over the range 0.33–0.6 MV/cm.
Journal of Electronic Materials, 2008
The general approach and effects of nonequilibrium operation of Auger-suppressed HgCdTe infrared ... more The general approach and effects of nonequilibrium operation of Auger-suppressed HgCdTe infrared photodiodes are well understood. However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent the development of simplistic analytical device models with acceptable accuracy. In this work, finite element methods are used to obtain self-consistent steady-state solutions of Poisson’s equation and
SPIE Proceedings, 2010
High sensitivity HgCdTe infrared detector arrays operating at 77 K can be tailored for response a... more High sensitivity HgCdTe infrared detector arrays operating at 77 K can be tailored for response across the infrared spectrum (1 to 14 mum and beyond), and are commonly utilized for high performance infrared imaging applications. However, the cooling system required to achieve the desired sensitivity makes them costly, heavy and limits their applicability. Reducing cooling requirements and eventually operating at
Journal of Crystal Growth, 1997
ABSTRACT
Journal of Applied Physics, 2012
Journal of Electronic Materials, 2008
Infrared Technology and Applications XXXVI, 2010
Low-Dimensional Materials and Devices, 2015
The majority of modern infrared photon imaging devices are based on epitaxially grown bulk semico... more The majority of modern infrared photon imaging devices are based on epitaxially grown bulk semiconductor materials. Colloidal quantum dot (CQD)-based infrared devices provide great promise for significantly reducing cost as well as significantly increased operating temperatures of infrared imaging systems. In addition, CQD-based infrared devices greatly benefit from band gap tuning by controlling the CQD size rather than the composition. In this work, we investigate the absorption coefficient of HgTe CQD films as a function of temperature and cutoff wavelength. The optical absorption properties are predicted for defect-free HgTe films as well as films which vary from ideal.
SPIE Proceedings, 2013
ABSTRACT Mid-wavelength infrared (MWIR) InAsSb alloy barrier detectors grown on GaAs substrates w... more ABSTRACT Mid-wavelength infrared (MWIR) InAsSb alloy barrier detectors grown on GaAs substrates were characterized as a function of temperature to evaluate their performance. Detector arrays were fabricated in a 1024 × 1024 format on an 18 μm pitch. A fanout was utilized to directly acquire data from a set of selected detectors without an intervening read out integrating circuit (ROIC). The detectors have a cutoff wavelength equal to ~ 4.9 μm at 150 K. The peak internal quantum efficiency (QE) required a reverse bias voltage of 1 V. The detectors were diffusion-limited at the bias required to attain peak QE. Multiple 18 μm × 18 μm detectors were tied together in parallel by connecting the indium bump of each detector to a single large metal pad on the fanout. The dark current density at -1 V bias for a set of 64 × 64 and 6 × 6 array of detectors, each of which were tied together in parallel was ~ 10-3 A/cm2 at 200 K and 5 × 10-6 A/cm2 at 150 K. The 4096 (64 × 64) and 36 (6 × 6) detectors, both have similar Jdark vs Vd characteristics, demonstrating high operability and uniformity of the detectors in the array. The external QE measured using a narrow band filter centered at ~ 4 μm had values in the 65 - 70 % range. Since the detectors were illuminated through a GaAs substrate which has a reflectance of 29%, the internal QE is greater than 90 %. A 1024 × 1024 ROIC on an 18 μm pitch was also designed and fabricated to interface with the barrier detectors. QE at 150 K for a 1024 × 1024 detector array hybridized to a ROIC matched the QE measured on detectors that were measured directly through a fanout chip. Median D* at 150 K under a flux of 1.07 × 1015 ph/(cm2/s was 1.0 x 1011 cm Hz1/2 /W.
Quantum Sensing and Nanophotonic Devices X, 2013
ABSTRACT Spatial noise and the loss of photogenerated current due material non-uniformities limit... more ABSTRACT Spatial noise and the loss of photogenerated current due material non-uniformities limit the performance of long wavelength infrared (LWIR) HgCdTe detector arrays. Reducing the electrical activity of defects is equivalent to lowering their density, thereby allowing detection and discrimination over longer ranges. Infrared focal plane arrays (IRFPAs) in other spectral bands will also benefit from detectivity and uniformity improvements. Larger signal-to-noise ratios permit either improved accuracy of detection/discrimination when an IRFPA is employed under current operating conditions, or provide similar performance with the IRFPA operating under less stringent conditions such as higher system temperature, increased system jitter or damaged read out integrated circuit (ROIC) wells. The bulk passivation of semiconductors with hydrogen continues to be investigated for its potential to become a tool for the fabrication of high performance devices. Inductively coupled plasmas have been shown to improve the quality and uniformity of semiconductor materials and devices. The retention of the benefits following various aging conditions is discussed here.
Materials for Infrared Detectors, 2001
The advantages of mercury cadmium telluride for 'HOT&... more The advantages of mercury cadmium telluride for 'HOT' IR detector applications are discussed. Molecular beam epitaxy (MBE) is used to grow advanced device structures for this purpose. MBE offers the potential to grow HgCdTe heterostructure layers on large silicon substrates leading to very large format and high performance IR focal plane array sin the future. Preliminary material and device properties
Journal of Electronic Materials, 1999
The p-type doping of Hg 1-x Cd x Te (MCT) has proven to be a significant challenge in present day... more The p-type doping of Hg 1-x Cd x Te (MCT) has proven to be a significant challenge in present day MCT-based detector technology. One of the most promising acceptor candidates, arsenic, behaves as an amphoteric dopant which can be activated as an acceptor during Hg-rich, low temperature annealing of as-grown molecular beam epitaxy (MBE) samples. This study focuses on developing an understanding of the microscopic behavior of arsenic incorporation during MBE growth. In particular, the question of whether arsenic incorporates as individual As atoms, as As 2 dimers, or as As 4 tetramers is addressed for MBE growth with an As 4 source. A quasithermodynamical model is employed to describe the MCT growth and As incorporation, with parameters fitted to an extensive database of samples grown at the Microphysics Laboratory. The best fits for growth temperatures between 175 and 185 o C are obtained for arsenic incorporation as As 4 or possibly as As 4 clusters, with lower probabilities for As 2 and individual As atoms. Based on these results, we investigate the relaxed atomic configurations of As 4 and As 2 in bulk HgTe by ab initio total energy calculations. The calculations are performed in the pseudopotential density-functional framework within the local density approximation, employing supercells with periodic boundary conditions. The lattice distortions due to As 4 and As 2 in bulk HgTe are predicted to be modest due to the small size of these arsenic clusters.
Applied Physics Letters, 2003
Crater defects on the surfaces of HgCdTe epilayers grown by molecular beam epitaxy have been inve... more Crater defects on the surfaces of HgCdTe epilayers grown by molecular beam epitaxy have been investigated. A semiempirical model coupled with observations by transmission electron microscopy was used to analyze the defect formation mechanism. We find that Te2 dissociation plays an important role. The defect density can be controlled by adjusting growth conditions such as the substrate growth temperature, Hg
Physical Review B, 1984
A generalization of the simplest Lifshitz-point model for a system with a real, one-component ord... more A generalization of the simplest Lifshitz-point model for a system with a real, one-component order parameter depending on a single coordinate is studied in mean-field theory and shown to yield two stable types of incommensurate states: one in which the order parameter oscillates about zero, and the other (the rippled commensurate state) in which it oscillates about a value somewhat less than the commensurate value.
We report temperature-dependent absorption measurements from 300 K to 4.2 K for molecular beam ep... more We report temperature-dependent absorption measurements from 300 K to 4.2 K for molecular beam epitaxy (MBE)-grown Hg 1x Cd x Te samples with different alloy compositions. The infrared absorption coefficients near the energy gap were obtained using an interference matrix method. Photoconductive spectra were simultaneously measured at the same points on the samples to precisely determine the energy gaps. The Urbach tail energies are extracted from the absorption coefficients, and their temperature dependence is analyzed using a theoretical model. The contribution from static disorder, including structural and alloy disorder, is found to be much larger than the phonon-related dynamic disorder.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2005
ABSTRACT InAs/GaSb superlattices are leading candidates for next generation long-wave infrared an... more ABSTRACT InAs/GaSb superlattices are leading candidates for next generation long-wave infrared and very-long-wave infrared photodetectors. These heterostructures are expected to hold important advantages over existing materials systems, primarily bulk HgCdTe alloys. To realize their inherent potential, however, superlattice materials with low defect density and improved device characteristics must be demonstrated. Here, we report on the molecular beam epitaxy growth and characterization of an 11 µm cutoff wavelength InAs/GaSb superlattice detector with a state-of-the-art single-pass, internal quantum efficiency of 36%. The shutter sequencing used to form the GaSb-on-InAs and InAs-on-GaSb superlattice heterojunctions is described in detail, and the latter specifically identified as a source of morphological defects in these devices. © 2005 American Vacuum Society.
Infrared Technology and Applications XXXI, 2005
ABSTRACT InAs-GaSb strained layer superlattices (SLSs) form a narrow band gap material whose cut-... more ABSTRACT InAs-GaSb strained layer superlattices (SLSs) form a narrow band gap material whose cut-off wavelength can be tuned from 3 um to beyond 30 um. Theory predicts that in the LWIR and VLWIR, the SLS narrow bandgap layer structures can be engineered to reduce Auger recombination, relative to other narrow bandgap materials, such as HgCdTe. This should result in the SLS diodes having better performance than currently available detectors. A key to achieving this improved performance is knowing the detailed layer structure of the superlattice, and being able to accurately model this layer structure. Having an accurate model to guide the improved performance is essential to optimizing this material system. Cross-sectional scanning tunneling microscopy data will be presented which shows that the actual layer structure differs significantly from the intended layer structure, due to the detailed dynamics of MBE growth and the very thin layers in the superlattice. Specifically, cross-sectional scanning tunneling microscopy demonstrates that the InAs contains excess antimony, and the GaSb excess indium, due to segregation from the underlying arsenide-on-antimonide, or antimonide-on-arsenide, heterojunctions respectively. These deviations from the intended structure have a significant impact on the predicted properties of the superlattice. The predicted behavior of the intended and actual superlattice structures will be compared to measured performance.
1999 IEEE LEOS Annual Meeting Conference Proceedings. LEOS'99. 12th Annual Meeting. IEEE Lasers and Electro-Optics Society 1999 Annual Meeting (Cat. No.99CH37009), 1999
ABSTRACT
IGARSS 2023 - 2023 IEEE International Geoscience and Remote Sensing Symposium
Physical Review B, 2012
Employing ab initio thermodynamics calculations, we elucidate for the first time the effects of g... more Employing ab initio thermodynamics calculations, we elucidate for the first time the effects of growth conditions on the reconstruction phase diagram of the polar Cd-terminated CdTe (111) surface and resolve an existing experimental controversy of the low-temperature reconstruction under Te-rich conditions. We demonstrate that the Cd-vacancy (2 × 2) reconstruction is the most stable configuration in the allowed range of the Te chemical potential. Under Te-rich conditions, however, the calculations reveal a transition from a high-temperature semiconducting (2 × 2) to a low-temperature metallic (1 × 1)-Te n reconstruction consisting of n Te adlayers forming a spiral trigonal structure. We also predict the temperature and pressure dependence of the Te thickness adlayer, which has remained experimentally unresolved.
Applied Physics Letters
For short-wavelength infrared (SWIR) avalanche photodiodes, a separate absorption, charge, and mu... more For short-wavelength infrared (SWIR) avalanche photodiodes, a separate absorption, charge, and multiplication design is widely used. AlInAsSb on an InP substrate is a potential multiplication layer with a lattice match to absorber candidates across the SWIR. Our new measurements demonstrate that AlInAsSb on InP is a promising multiplier candidate with a relatively low dark current density of 10−4 A/cm2 at a gain of 30; a high gain, measured up to 245 in this study; and a large differentiation of electron and hole ionization leading to a low excess noise, measured to be 2.5 at a gain of 30. These characteristics are all improvements over commercially available SWIR detectors incorporating InAlAs or InP as the multiplier. We measured and analyzed gain for multiple wavelengths to extract the ionization coefficients as a function of an electric field over the range 0.33–0.6 MV/cm.
Journal of Electronic Materials, 2008
The general approach and effects of nonequilibrium operation of Auger-suppressed HgCdTe infrared ... more The general approach and effects of nonequilibrium operation of Auger-suppressed HgCdTe infrared photodiodes are well understood. However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent the development of simplistic analytical device models with acceptable accuracy. In this work, finite element methods are used to obtain self-consistent steady-state solutions of Poisson’s equation and
SPIE Proceedings, 2010
High sensitivity HgCdTe infrared detector arrays operating at 77 K can be tailored for response a... more High sensitivity HgCdTe infrared detector arrays operating at 77 K can be tailored for response across the infrared spectrum (1 to 14 mum and beyond), and are commonly utilized for high performance infrared imaging applications. However, the cooling system required to achieve the desired sensitivity makes them costly, heavy and limits their applicability. Reducing cooling requirements and eventually operating at
Journal of Crystal Growth, 1997
ABSTRACT
Journal of Applied Physics, 2012
Journal of Electronic Materials, 2008
Infrared Technology and Applications XXXVI, 2010
Low-Dimensional Materials and Devices, 2015
The majority of modern infrared photon imaging devices are based on epitaxially grown bulk semico... more The majority of modern infrared photon imaging devices are based on epitaxially grown bulk semiconductor materials. Colloidal quantum dot (CQD)-based infrared devices provide great promise for significantly reducing cost as well as significantly increased operating temperatures of infrared imaging systems. In addition, CQD-based infrared devices greatly benefit from band gap tuning by controlling the CQD size rather than the composition. In this work, we investigate the absorption coefficient of HgTe CQD films as a function of temperature and cutoff wavelength. The optical absorption properties are predicted for defect-free HgTe films as well as films which vary from ideal.
SPIE Proceedings, 2013
ABSTRACT Mid-wavelength infrared (MWIR) InAsSb alloy barrier detectors grown on GaAs substrates w... more ABSTRACT Mid-wavelength infrared (MWIR) InAsSb alloy barrier detectors grown on GaAs substrates were characterized as a function of temperature to evaluate their performance. Detector arrays were fabricated in a 1024 × 1024 format on an 18 μm pitch. A fanout was utilized to directly acquire data from a set of selected detectors without an intervening read out integrating circuit (ROIC). The detectors have a cutoff wavelength equal to ~ 4.9 μm at 150 K. The peak internal quantum efficiency (QE) required a reverse bias voltage of 1 V. The detectors were diffusion-limited at the bias required to attain peak QE. Multiple 18 μm × 18 μm detectors were tied together in parallel by connecting the indium bump of each detector to a single large metal pad on the fanout. The dark current density at -1 V bias for a set of 64 × 64 and 6 × 6 array of detectors, each of which were tied together in parallel was ~ 10-3 A/cm2 at 200 K and 5 × 10-6 A/cm2 at 150 K. The 4096 (64 × 64) and 36 (6 × 6) detectors, both have similar Jdark vs Vd characteristics, demonstrating high operability and uniformity of the detectors in the array. The external QE measured using a narrow band filter centered at ~ 4 μm had values in the 65 - 70 % range. Since the detectors were illuminated through a GaAs substrate which has a reflectance of 29%, the internal QE is greater than 90 %. A 1024 × 1024 ROIC on an 18 μm pitch was also designed and fabricated to interface with the barrier detectors. QE at 150 K for a 1024 × 1024 detector array hybridized to a ROIC matched the QE measured on detectors that were measured directly through a fanout chip. Median D* at 150 K under a flux of 1.07 × 1015 ph/(cm2/s was 1.0 x 1011 cm Hz1/2 /W.
Quantum Sensing and Nanophotonic Devices X, 2013
ABSTRACT Spatial noise and the loss of photogenerated current due material non-uniformities limit... more ABSTRACT Spatial noise and the loss of photogenerated current due material non-uniformities limit the performance of long wavelength infrared (LWIR) HgCdTe detector arrays. Reducing the electrical activity of defects is equivalent to lowering their density, thereby allowing detection and discrimination over longer ranges. Infrared focal plane arrays (IRFPAs) in other spectral bands will also benefit from detectivity and uniformity improvements. Larger signal-to-noise ratios permit either improved accuracy of detection/discrimination when an IRFPA is employed under current operating conditions, or provide similar performance with the IRFPA operating under less stringent conditions such as higher system temperature, increased system jitter or damaged read out integrated circuit (ROIC) wells. The bulk passivation of semiconductors with hydrogen continues to be investigated for its potential to become a tool for the fabrication of high performance devices. Inductively coupled plasmas have been shown to improve the quality and uniformity of semiconductor materials and devices. The retention of the benefits following various aging conditions is discussed here.
Materials for Infrared Detectors, 2001
The advantages of mercury cadmium telluride for 'HOT&... more The advantages of mercury cadmium telluride for 'HOT' IR detector applications are discussed. Molecular beam epitaxy (MBE) is used to grow advanced device structures for this purpose. MBE offers the potential to grow HgCdTe heterostructure layers on large silicon substrates leading to very large format and high performance IR focal plane array sin the future. Preliminary material and device properties
Journal of Electronic Materials, 1999
The p-type doping of Hg 1-x Cd x Te (MCT) has proven to be a significant challenge in present day... more The p-type doping of Hg 1-x Cd x Te (MCT) has proven to be a significant challenge in present day MCT-based detector technology. One of the most promising acceptor candidates, arsenic, behaves as an amphoteric dopant which can be activated as an acceptor during Hg-rich, low temperature annealing of as-grown molecular beam epitaxy (MBE) samples. This study focuses on developing an understanding of the microscopic behavior of arsenic incorporation during MBE growth. In particular, the question of whether arsenic incorporates as individual As atoms, as As 2 dimers, or as As 4 tetramers is addressed for MBE growth with an As 4 source. A quasithermodynamical model is employed to describe the MCT growth and As incorporation, with parameters fitted to an extensive database of samples grown at the Microphysics Laboratory. The best fits for growth temperatures between 175 and 185 o C are obtained for arsenic incorporation as As 4 or possibly as As 4 clusters, with lower probabilities for As 2 and individual As atoms. Based on these results, we investigate the relaxed atomic configurations of As 4 and As 2 in bulk HgTe by ab initio total energy calculations. The calculations are performed in the pseudopotential density-functional framework within the local density approximation, employing supercells with periodic boundary conditions. The lattice distortions due to As 4 and As 2 in bulk HgTe are predicted to be modest due to the small size of these arsenic clusters.
Applied Physics Letters, 2003
Crater defects on the surfaces of HgCdTe epilayers grown by molecular beam epitaxy have been inve... more Crater defects on the surfaces of HgCdTe epilayers grown by molecular beam epitaxy have been investigated. A semiempirical model coupled with observations by transmission electron microscopy was used to analyze the defect formation mechanism. We find that Te2 dissociation plays an important role. The defect density can be controlled by adjusting growth conditions such as the substrate growth temperature, Hg
Physical Review B, 1984
A generalization of the simplest Lifshitz-point model for a system with a real, one-component ord... more A generalization of the simplest Lifshitz-point model for a system with a real, one-component order parameter depending on a single coordinate is studied in mean-field theory and shown to yield two stable types of incommensurate states: one in which the order parameter oscillates about zero, and the other (the rippled commensurate state) in which it oscillates about a value somewhat less than the commensurate value.
We report temperature-dependent absorption measurements from 300 K to 4.2 K for molecular beam ep... more We report temperature-dependent absorption measurements from 300 K to 4.2 K for molecular beam epitaxy (MBE)-grown Hg 1x Cd x Te samples with different alloy compositions. The infrared absorption coefficients near the energy gap were obtained using an interference matrix method. Photoconductive spectra were simultaneously measured at the same points on the samples to precisely determine the energy gaps. The Urbach tail energies are extracted from the absorption coefficients, and their temperature dependence is analyzed using a theoretical model. The contribution from static disorder, including structural and alloy disorder, is found to be much larger than the phonon-related dynamic disorder.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2005
ABSTRACT InAs/GaSb superlattices are leading candidates for next generation long-wave infrared an... more ABSTRACT InAs/GaSb superlattices are leading candidates for next generation long-wave infrared and very-long-wave infrared photodetectors. These heterostructures are expected to hold important advantages over existing materials systems, primarily bulk HgCdTe alloys. To realize their inherent potential, however, superlattice materials with low defect density and improved device characteristics must be demonstrated. Here, we report on the molecular beam epitaxy growth and characterization of an 11 µm cutoff wavelength InAs/GaSb superlattice detector with a state-of-the-art single-pass, internal quantum efficiency of 36%. The shutter sequencing used to form the GaSb-on-InAs and InAs-on-GaSb superlattice heterojunctions is described in detail, and the latter specifically identified as a source of morphological defects in these devices. © 2005 American Vacuum Society.
Infrared Technology and Applications XXXI, 2005
ABSTRACT InAs-GaSb strained layer superlattices (SLSs) form a narrow band gap material whose cut-... more ABSTRACT InAs-GaSb strained layer superlattices (SLSs) form a narrow band gap material whose cut-off wavelength can be tuned from 3 um to beyond 30 um. Theory predicts that in the LWIR and VLWIR, the SLS narrow bandgap layer structures can be engineered to reduce Auger recombination, relative to other narrow bandgap materials, such as HgCdTe. This should result in the SLS diodes having better performance than currently available detectors. A key to achieving this improved performance is knowing the detailed layer structure of the superlattice, and being able to accurately model this layer structure. Having an accurate model to guide the improved performance is essential to optimizing this material system. Cross-sectional scanning tunneling microscopy data will be presented which shows that the actual layer structure differs significantly from the intended layer structure, due to the detailed dynamics of MBE growth and the very thin layers in the superlattice. Specifically, cross-sectional scanning tunneling microscopy demonstrates that the InAs contains excess antimony, and the GaSb excess indium, due to segregation from the underlying arsenide-on-antimonide, or antimonide-on-arsenide, heterojunctions respectively. These deviations from the intended structure have a significant impact on the predicted properties of the superlattice. The predicted behavior of the intended and actual superlattice structures will be compared to measured performance.
1999 IEEE LEOS Annual Meeting Conference Proceedings. LEOS'99. 12th Annual Meeting. IEEE Lasers and Electro-Optics Society 1999 Annual Meeting (Cat. No.99CH37009), 1999
ABSTRACT