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InAsSb material with a cutoff wavelength in the 5 μm range has been grown on GaAs substrates. The MWIR InAsSb detector arrays were fabricated and hybridized to a ROIC to permit measurement of the electrical and optical properties of detectors. Detector arrays were fabricated in a 1024 x 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). Variable temperature Jdark vs Vd measurements have been made with the dark current density ~ 10-5 A/cm 2 at 150 K. 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 x 1024 ROIC on an 18 μm pitch was also designed and fabricated to interface with the barrier detectors. The ROIC operates at 30 Hz frame rate and has a well capacity of 20.7 M electrons. QE at 150 K for a 1024 x 1024 detector array hybridized to a ROIC had a median D* at 150 K under a flux of 1.07 x 1015 ph/(cm 2 /s) was 1.2 x 1011 cm Hz1/2 /W. The NEdT was 44 mK and imagery was obtained at 150 K using an f/2.3 MWIR lens.

InAsSb material with a cutoff wavelength in the 5 μm range has been grown on GaAs substrates. The MWIR InAsSb detector arrays were fabricated and hybridized to fanouts and ROICs to permit measurement of the electrical and optical properties of detectors. Detector arrays were fabricated in a 1024 x 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). Variable temperature Jdark vs Vd measurements have been made with the dark current density ~ 10 -5 A/cm 2 at 150 K. 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 x 1024 ROIC on an 18 μm pitch was also designed and fabricated to interface with the barrier detectors. The ROIC operates at 30 Hz frame rate and has a well capacity of 20.7 M electrons. QE at 150 K for a 1024 x 1024 detector array hybridized to a ROIC had a median D* at 150 K under a flux of 1.07 x 10 15 ph/(cm 2 /s was 1.2 x 10 11 cm Hz 1/2 /W. The NEdT was 44 mK and imagery was obtained at 150 K using an f/2.3 MWIR lens.

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.

We describe our recent efforts in developing visible to mid-wave (0.5 µm to 5.0 µm) broadband photon-trap InAsSb-based infrared detectors grown on GaAs substrates operating at high temperature (150-200K) with low dark current and high quantum efficiency. Utilizing an InAsSb absorber on GaAs substrates instead of an HgCdTe absorber will enable low-cost fabrication of large-format, high operating temperature focal plane arrays. We have utilized a novel detector design based-on pyramidal photon trapping InAsSb structures in conjunction with compound barrier-based device architecture to suppress both G-R dark current, as well as diffusion current through absorber volume reduction. Our optical simulation show that our engineered pyramid structures minimize the surface reflection compared to conventional diode structures acting as a broadband anti-reflective coating (AR). In addition, it exhibits > 70-80% absorption over the entire 0.5 µm to 5.0 µm spectral range while providing up to 3× reduction in absorber volume. Lattice-mismatched InAs0.82Sb0.18 with 5.25 µm cutoff at 200K was grown on GaAs substrates. 128×128/60μm and 1024×1024/18μm detector arrays that consist of bulk absorber as well as photon-trap pyramid structures were fabricated to compare the detector performance. The measured dark current density for the diodes with the pyramidal absorber was 3× lower that for the conventional diode with the bulk absorber, which is consistent with the volume reduction due to the creation of the pyramidal absorber topology. We have achieved high D* (< 1.0 x 1010 cm √Hz/W) and maintain very high (< 80 %) internal quantum efficiency over the entire band 0.5 to 5 µm spectral band at 200K.

In InAs1-xSbx material alloy composition was adjusted to achieve 200K cutoff wavelengths in the 5 mm range. Reflectance was minimized and absorption in the InAs1-xSbx material maximized by the use of pyramid shaped structures fabricated in the InAs1-xSbx material which function as an AR coating. Compound-barrier (CB) detectors were fabricated and tested for optical response and dark current density versus bias measurements were acquired as a function of temperature. For 5 mm cutoff detectors, QE is high, ~ 75 % between 4.0 mm and 4.6 mm and g 80 % between 2.0 mand 4.0 mm, demonstrating the efficacy of the pyramids as photon trap structures and as a replacement for multi-layer AR-coatings. Jdark in the low 10-3 A/cm2 range at 200 K and low 10-5 A/cm2 range at 150 K was measured at the bias at which the QE peaked.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

United States. Defense Advanced Research Projects Agency (DARPA under contract N66604-09-C-3652)

Recent efforts in developing InAs/GaSb strained-layer superlattices for LWIR detectors are described. The structural properties of the devices grown by MBE at HRL were evaluated using optical microscopy, x-ray diffraction, and atomic force microscopy. Epilayer roughness and surface morphology are briefly described. Small format focal plane arrays were fabricated to serve as a baseline for device study, and to determine the effects of underfill epoxy on detector performance. A novel approach for epilayer transfer on silicon is also presented.

We have designed and evaluated (using computer simulations) several different 2D phased arrays with square elements for deep localized hyperthermia. These array include a 20x20 planar array, a 80x16 cylindrical-section array, and a 16x16 spherical-section array. Also, we have designed a new phased array with circular elements. We used single and multiple focus scanning methods with intensity gain maximization. We found that the array with circular elements is more effective in reducing grating lobes compared to the same array with square elements. The grating lobes were at least 30 dB smaller than the phased array with square elements and intensity gain was at least 1 dB greater. In addition, with equal intensity distribution patterns for rectangular and circular phased arrays, the number of elements in the circular phased array was smaller and its intensity gain was greater than the other arrays.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.