Search

Avalanche photodiodes (APDs) are well-suited for single-photon detection on quantum communication satellites as they are a mature technology with high detection efficiency without requiring cryogenic cooling. They are, however, prone to significantly increased thermal noise caused by in-orbit radiation damage. Previous work demonstrated that a one-time application of thermal annealing reduces radiation-damage-induced APD thermal noise. Here we examine the effect of cyclical proton irradiation and thermal annealing. We use an accelerated testing environment which emulates a realistic two-year operating profile of a satellite in low-Earth-orbit. We show that repeated thermal annealing is effective at maintaining thermal noise of silicon APDs within a range suitable for quantum key distribution throughout the nominal mission life, and beyond. We examine two strategies -- annealing at a fixed period of time, and annealing only when the thermal noise exceeds a pre-defined limit. We find both strategies exhibit similar thermal noise at end-of-life, with a slight overall advantage to annealing conditionally. We also observe that afterpulsing probability of the detector increases with cumulative proton irradiation. This knowledge helps guide design and tasking decisions for future space-borne quantum communication applications., Comment: 7 pages, 8 figures

High Density Vertically Integrated Photodiodes (HDVIP) MWIR detectors were fabricated in LPE-grown Mercury Cadmium Telluride material. Devices were fabricated with two different acceptor level concentrations. The low doped n-region was held at a single concentration but the dimensions are tailored to simultaneously maintain high quantum efficiency while minimizing dark current and 1/f noise. Since this study target was for operating at high temperatures, detector I-V data was collected between 120 K and 280 K for I-Vs and 180 to 280 K for noise to understand current mechanisms that limit device performance at these elevated temperatures. Noise as a function of frequency has also been collected over the same temperature range. 1/f noise has also been modeled for MWIR detectors as a function of temperature and will be covered.

Weather satellite instruments require detectors with a variety of wavelengths ranging from the visible to VLWIR. The Cross-track infrared Sounder (CrIS) is a Polar Orbiting interferometric sensor that measures earth radiances at high spectral resolution, using the data to provide pressure, temperature and moisture profiles of the atmosphere. The pressure, temperature and moisture sounding data are used in weather prediction models that track storms, predict levels of precipitation etc. The CrIS instrument contains SWIR (lambda(sub c) (is) approximately 5 micrometers at 98 K), MWIR (lambda(sub c) (is) approximately 9 micrometers at 98 K) and LWIRs (lambda(sub c) (is) approximately 15.4 m at 81 K) bands in three Focal Plane Array Assemblies (FPAAs). CrIS detectors are 850 micrometers diameter detectors with each FPAA consisting of nine photovoltaic detectors arranged in a 3 x 3 pattern. Molecular beam epitaxy (MBE)-grown Hg1-xCdxTe material are used for the detectors fabricated in a modified Double Layer Planar Heterostructure (DLPH) architecture. Each detector has an accompanying cold preamplifier. SWIR and MWIR FPAAs operate at 98 K and the LWIR FPAA at 81 K, permitting the use of passive radiators to cool the detectors. D* requirements at peak 14.01 micrometers wavelength are greater than 5.0E+10 Jones for LWIR, greater than 7.5E+10 Jones at 8.26 micrometers for MWIR and greater than 3.0E+11 Jones at peak 4.64 micrometers wavelength for SWIR. All FPAAs exceeded the D* requirements. Measured mean values for the nine photodiodes in each of the LWIR, MWIR and SWIR FPAAs are D* = 5.3 x 10(exp 10) cm-Hz1/2/W at 14.0 micrometers, 9.6 x 10(exp 10) cm-Hz1/2/W at 8.0 micrometers and 3.4 x 10(exp 11) cm-Hz1/2/W at 4.64 micrometers.

Weather satellite instruments require detectors with a variety of wavelengths ranging from the visible to VLWIR. One of the remote sensing applications is the geostationary GOES-ABI imager covering wavelengths from the 450 to 490 nm band through the 13.0 to 13.6 μm band. There are a total of 16 spectral bands covered. The Cross-track infrared Sounder (CrIS) is a Polar Orbiting interferometric sensor that measures earth radiances at high spectral resolution, using the data to provide pressure, temperature and moisture profiles of the atmosphere. The pressure, temperature and moisture sounding data are used in weather prediction models that track storms, predict levels of precipitation etc. The CrIS instrument contains SWIR (λc ∼ 5 μm at 98K), MWIR (λc ∼ 9 μm at 98K) and LWIRs (λc ∼ 15.5 μm at 81K) bands in three Focal Plane Array Assemblies (FPAAs). GOES-ABI contains three focal plane modules (FPMs), (i) a visible-near infrared module consisting of three visible and three near infrared channels, (ii) a MWIR module comprised of five channels from 3.9 μm to 8.6 μm and (iii) a 9.6 μm to 13.3 μm, five-channel LWIR module. The VNIR FPM operates at 205 K, and the MWIR and LWIR FPMs operate at 60 K. Each spectral channel has a redundant array built into a single detector chip. Switching is thus permitted from the primary selected array in each channel to the redundant array, given any degradation in performance of the primary array during the course of the mission. Silicon p-i-n detectors are used for the 0.47 μm to 0.86 μm channels. The thirteen channels above 1 μm are fabricated in various compositions of Hg1-xCdxTe, and in this particular case using two different detector architectures. The 1.38 μm to 9.61 μm channels are all fabricated in Hg1-xCdxTe grown by Liquid Phase Epitaxy (LPE) using the HDVIP detector architecture. Molecular beam epitaxy (MBE)-grown Hg1-xCdxTe material are used for the LWIR 10.35 μm to 13.3 μm channels fabricated in Double layer planar heterostructure (DLPH) detectors. This is the same architecture used for the CrIS detectors. CrIS detectors are 850 μm diameter detectors with each FPAA consisting of nine photovoltaic detectors arranged in a 3 x 3 pattern. Each detector has an accompanying cold preamplifier. SWIR and MWIR FPAAs operate at 98 K and the LWIR FPAA at 81 K, permitting the use of passive radiators to cool the detectors. D* requirements at peak wavelength are ≥ 5.0E+10 Jones for LWIR, ≥ 9.3E+10 Jones for MWIR and ≥ 3.0E+11 Jones for SWIR. All FPAAs exceeded the D* requirements. Measured mean values for the nine photodiodes in each of the LWIR, MWIR and SWIR FPAAs are D* = 5.3 x 1010 cm-Hz1/2/W at 14.0 μm, 1.0 x 1011 cm-Hz1/2/W at 8.0 μm and 3.1 x 1011 cm-Hz1/2/W at 4.64 μm.

Improvement of bio-availability of poorly water soluble drugs presents one of the furthermost challenge in drug formulations. One of the most admired and commercially viable formulation approach for this challenge is solid self micro emulsifying drug delivery system (S-SMEDDS). There are many techniques to convert liquid SMEDDS to solid, but an adsorption technique is simple and economic. Hence aim of present study was to develop S-SMEDDS of poorly water soluble drug Telmisartan (TEL) using Aerosil 200 as solid carrier. Liquid SMEDDS was prepared using Acrysol EL 135, Tween 80 and PEG 400 as oil, surfactant and co-surfactant and was converted to S-SMEDDS by adsorbing it on Aerosil 200. Prepared S-SMEDDS was evaluated for flow properties, drug content, reconstitution properties, DSC, SEM, in-vitro drug release and ex-vivo intestinal permeability study. Results showed that prepared S-SMEDDS have good flow property with 99.45 ± 0.02% drug content. Dilution study by visual observation showed that there was spontaneous micro emulsification and no sign of phase separation. Droplet size was found to be 0.34 µm with polydispersity index of 0.25. DSC thermogram showed that crystallization of TEL was inhibited. SEM photograph showed smooth surface of S-SMEDDS with less aggregation. Drug releases from S- SMEDDS were found to be significantly higher as compared with that of plain TEL. Ex-vivo intestinal permeability study revealed that diffusion of drug was significantly higher from S-SMEDDS than that of suspension of plain TEL. Study concluded that S-SMEDDS can effectively formulated by adsorption technique with enhanced dissolution rate and concomitantly bioavailability.DOI: http://dx.doi.org/10.3329/icpj.v1i12.12451 International Current Pharmaceutical Journal 2012, 1(12): 414-419

An array of seven atmospheric Cherenkov telescopes was commissioned at a high altitude site in Hanle in the Ladakh region of the Himalayas. The array called HAGAR has been designed to observe celestial γ-rays of energy >100 GeV. Each telescope is altitude-azimuth mounted and carries seven parabolic mirrors whose optic axes are co-aligned with the telescope axis. The telescopes point and track a celestial source using a PC-based drive control system. Two important issues in positioning of each HAGAR telescope are pointing accuracy of telescope axis and co-alignment of mirrors’ optic axes with the telescope axis. We have adopted a three pronged strategy to address these issues, namely use of pointing models to improve pointing accuracy of the telescopes, RA-DEC scan technique to measure the pointing offsets of the mirrors and mechanical fine-tuning of off-axis mirrors by sighting a distant stationary light source. This paper discusses our efforts in this regard as well as the current status of pointing and monitoring of HAGAR telescopes.

Spectral response of detectors can be modeled using a stack matrix approach. The different material layers that make up the detector form the optical stack. Light intensity is proportional to the square of the amplitude of the electromagnetic field’s electric field component. Using the electric component of light, the model takes into account the reflective and transmission coefficients at the interface between two adjacent layers and the phase difference during propagation within each layer. The transition from one optical layer to another and the propagation within an optical layer can be formulated as 2 × 2 matrices; their multiplication through every optical layer makes up the stack matrix that defines the optical properties of the detector. Knowing the complex index of refraction for each layer in the detector, the intensity of light can be calculated at any point in the detector structure, which can then be used to determine the response of the detector as a function of wavelength. This model shows fairly good agreement with the experimental data, even revealing fine structure and etalon effects. Using this model, the detector can be designed to meet specific spectral characteristics. The spectral response model was used on high-density vertically interconnected photodiode front-side-illuminated photodiodes.

The Cross-Track Infrared Sounder (CrIS) program [an instrument on the National Polar-Orbiting Operational Environmental Satellite System (NPOESS)] requires photodiodes with spectral cutoffs denoted by short-wavelength infrared [γc(98 K) ∼5.1 µm], midwavelength infrared [γc(98 K) ∼9.1 µm], and long-wavelength infrared (LWIR) [γc(81 K) ∼15.5 µm]. The CrIS instrument also requires large-area (850-µm-diameter) photodiodes with state-of-art performance. Molecular beam epitaxy (MBE) is used to grow n-type short-wavelength infrared, midwavelength infrared, or LWIR Hg1−xCdxTe on latticematched CdZnTe. Detectors with p-type implants 7 µm in diameter are used to constitute the 850-µm-diameter lateral collection diodes (LCDs). The photodiode architecture is the double-layer planar heterostructure architecture.

The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg1−xCdxTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of 1000-µm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The 1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density in the mid-10−15A/Hz1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth in(f = 1 Hz, Vd = −60 mV, and Δf = 1 Hz) to dark current Id(Vd = −60 mV) was αSW-d = in/Id ∼ 1 × 10−3. The SWIR detectors measured at 0 mV under illuminated conditions had median αSW-P = in/Iph ∼ 7 × 10−6. For mid-wave infrared (MWIR) detectors, αMW-d = in/Id ∼ 2 × 10−4, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-µm-diameter MWIR detectors under illuminated conditions at 98 K and −60 mV bias resulted in αMW-P = in/Iph = 4.16 ± 1.69 × 10−6. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise-current-to-photocurrent ratio, αMW-P, in the mid 10−6 range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, αLW-d = in/Id ∼ 6 × 10−6, for the best performers. The majority of the LWIR detectors exhibited αLW-d on the order of 2 × 10−5. The photo-induced 1/f noise had αLW-P = in/Iph ∼ 5 × 10−6. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular bias. The 1/f noise was not a direct function of the applied bias.

This paper investigates 1/f noise performance of very-long-wavelength infrared (VLWIR) Hg1-xCdxTe (cutoff wavelengths λc = 15 µm and λc = 16 µm) photodiodes at 78 K, where detector current is varied by changing detector area, detector bias, and illumination conditions. Holding detector bias and temperature constant, the 1/f noise current is proportional to the detector current. Significant nonuniformity is observed in the noise data for each detector area because of the varying detector quality. Defects are presumed resident in the detectors to produce greater nonuniformity in 1/f noise as compared to dark current at 100-mV reverse bias. For λc = 16 µm, 4-µm-radius, diffusion-limited diodes at 78 K and 100-mV reverse bias, the average dark current is Id = 9.76 ± 1.59 × 10-8A, while the average noise current measured at 1 Hz is in = 1.01 ± 0.63 × 10-12A/Hz1/2. For all detector areas measured, the average ratio in 1-Hz bandwidth is αD = in/Id = 1.39 ± 1.09 × 10-5. The 1/f noise was also measured on one diode as a function of detector-dark current as the applied bias is varied. In the diffusion-limited portion of this detector's current-voltage (I-V) curve, to about 130 mV, the 1/f noise was independent of bias. For this diode, the ratio αD = in/Id = 1.51 ± 0.12 × 10-5. The 1/f noise associated with tunneling currents is a factor of 3 greater than the 1/f noise associated with diffusion currents, αT = in/IT = 5.21 ± 0.83 × 10-5. In addition, 1/f noise was measured on detectors held at - 100 mV and 78 K under dark and illuminated conditions. The measured ratios αp ∼ αD ∼ 1.5 × 10-5 were about the same for the dark and photon-induced diffusion currents. Therefore, the diffusion current appears to have a unique value of α as compared to the tunneling current. This may be indicative of unique noise-generation mechanisms associated with each current.

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.

The current-voltage characteristics and quantum efficiencies of double layer planar heterostructure photodiodes were investigated. Results are reported on devices with cutoff wavelengths of 1.8, 2.4, and 3.3 µm. For these respective devices, the dominant currents for temperatures >250,>200,>150K are diffusion currents limited by shallow Shockley-Hall-Read (SHR) processes. The remarkable result is that the electrical and optoelectronic properties of these devices of diverse cut-off wavelength can be explained by simple models using independently measured layer parameters such as the minority carrier lifetimes. For all three cases, the analysis suggests that the same shallow (SHR) centers located at 78% of the energy gap are causing the observed effects. These traps located in then-type base of the device are not influenced by the magnitude of n-type doping and this observation was used to significantly improve the performance of the devices and validate the predictive capability of the models used in the analysis. The shallow centers appear to be process induced rather than grown-in. This assertion is based on the observation that changes in the annealing process led to an order of magnitude improvement in the minority carrier lifetime.

The capability of growing state-of-the-art middle wavelength infrared (MWIR)-HgCdTe layers by molecular beam epitaxy (MBE) on large area silicon substrates has been demonstrated. We have obtained excellent compositional uniformity with standard deviation of 0.001 with mean composition of 0.321 across 1.5″ radii. R0A as high as 5 × 107 ω-cm2 with a mean value of 7 × 106 Θ-cm2 was measured for cut-off wavelength of 4.8 µm at 77K. Devices exhibit diffusion limited performance for temperatures above 95K. Quantum efficiencies up to 63% were observed (with no anti-reflection coating) for cut-off wavelength (4.8–5.4) µm @ 77K. Excellent performance of the fabricated photodiodes on MBE HgCdTe/CdTe/Si reflects on the overall quality of the grown material in the MWIR region.

Mid wavelength infrared p-on-n double layer planar heterostructure (DLPH) photodiodes have been fabricated in HgCdTe double layers grown in situ by liquid phase epitaxy (LPE), on CdZnTe and for the first time on CdTe/sapphire (PACE-1). Characterization of these devices shed light on the nature of the material limits on device performance for devices performing near theoretical limits. LPE double layers on CdZnTe and on PACE-1 substrates were grown in a horizontal slider furnace. All the photodiodes are p-on-n heterostructures with indium as the n-type dopant and arsenic the p-type dopant. Incorporation of arsenic is via implantation followed by an annealing step that was the same for all the devices fabricated. The devices are passivated with MBE CdTe. Photodiodes have been characterized as a function of temperature. R0Aimp values obtained between 300 and 78K are comparable for the two substrates and are approximately a factor of five below theoretical values calculated from measured material parameters. The data, for the PACE-1 substrate, indicates diffusion limited performance down to 110K. Area dependence gives further indications as to the origin of diffusion currents. Comparable R0Aimp for various diode sizes indicates a p-side origin. R0A and optical characteristics for the photodiodes grown on lattice-matched CdZnTe substrates and lattice mismatched PACE-1 are comparable. Howover, differences were observed in the noise characteristics of the photodiodes. Noise was measured on 50 × 50 µm devices held under a 100 mV reverse bias. At 110K, noise spectrum for devices from the two substrates is in the low 10−15 A/Hz1/2 range. This value reflects the Johnson noise of the room temperature 1010 Ω feedback resistor in the current amplifier that limits the minimum measurable noise. Noise at 1 Hz, −100 mV and 120K for the 4.95 µm PACE-1 devices is in the 1–2 × 10−14 A/Hz1/2, a factor of 5–10 lower than previously grown typical PACE-1 n+-on-p layers. Noise at 120K for the 4.60 µm PACE-1 and LPE on CdZnTe was again below the measurement technique limit. Greatest distinction in the noise characteristics for the different substrates was observed at 163K. No excess low frequency noise was observed for devices fabricated on layers grown by LPE on lattice-matched CdZnTe substrates. Photodiode noise measured at 1Hz, −100 mV and 163K in the 4.60 µm PACE-1 layer is in the 1–2×10−13 A/Hz1/2, again a factor of 5–10 lower than previously grown PACE-1 n+-on-p layers. More variation in noise (4×10−13−2×10−12 A/Hz1/2) was observed for devices in the 4.95 µm PACE-1 layer. DLPH devices fabricated in HgCdTe layers grown by LPE on lattice-matched CdZnTe and on lattice-mismatched PACE-1 have comparable R0A and quantum efficiency values. The distinguishing feature is that the noise is greater for devices fabricated in the layer grown on lattice mismatched substrates, suggesting dislocations inherent in lattice mismatched material affects excess low frequency noise but not zero bias impedance.

RTI has demonstrated a novel photodiode technology based on IR-absorbing solution-processed PbS colloidal quantum dots (CQD) that can overcome the high cost, limited spectral response, and challenges in the reduction in pixel size associated with InGaAs focal plane arrays. The most significant advantage of the CQD technology is ease of fabrication. The devices can be fabricated directly onto the ROIC substrate at low temperatures compatible with CMOS, and arrays can be fabricated at wafer scale. Further, device performance is not expected to degrade significantly with reduced pixel size. We present results for upward-looking detectors fabricated on Si substrates with sensitivity from the UV to ~1.7 μm, compare these results to InGaAs detectors, and present measurements of the CQD detectors temperature dependent dark current.

While InGaAs-based focal plane arrays (FPAs) provide excellent detectivity and low noise for SWIR imaging applications, wider scale adoption of systems capable of working in this spectral range is limited by high costs, limited spectral response, and costly integration with Si ROIC devices. RTI has demonstrated a novel photodiode technology based on IR-absorbing solution-processed PbS colloidal quantum dots (CQD) that can overcome these limitations of InGaAs FPAs. The most significant advantage of the CQD technology is ease of fabrication. The devices can be fabricated directly onto the ROIC substrate at low temperatures compatible with CMOS, and arrays can be fabricated at wafer scale. Further, device performance is not expected to degrade significantly with reduced pixel size. We present results for upward-looking detectors fabricated on Si substrates with sensitivity from the UV to ~1.7 µm. We further show devices fabricated with larger size CQDs that exhibit spectral sensitivity that extends from UV to 2 µm.

Silicon photon detectors and focal plane arrays (FPAs) are fabricated in many varieties 1,2 . Their function depends on the detector architecture, dopants, and operating temperature. DRS has fabricated silicon pin detectors that cover the visible spectral range and blocked impurity band (BIB) detectors that cover the very-long-wavelength infrared (VLWIR) region 3 . Imaging arrays of silicon pin-diodes utilize the intrinsic bandgap of silicon to provide high photo response over the 0.4 – 1.0 μm spectral range. The detectors operate at or near room temperature as required. Silicon pin -diode arrays are particularly attractive as an alternative to charge-coupled devices (CCDs) for space applications where radiation hardening is needed. Pros and cons of CCD and pin diode architectures are listed in Reference 4 .

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.

The photocurrent of High Density Vertically Integrated Photodiodes (HDVIP) manufactured in LPE grown SWIR (λc ~ 2.5 μm) HgCdTe material is modeled as a function of incident spot location using a Monte Carlo diffusion calculation in the p-type bulk. The Monte Carlo calculation assumes a 3 x 3 mini-array of detectors surrounded by guard detectors. Carriers generated in the n-regions are always collected. The result is a responsivity map that yields the individual detector "spot scan" profile that is then used to calculate the detector modulation transfer function (MTF). Fourier transforms of detector "spot scan" response profile provided experimental confirmation of MTF that corresponded to the Monte Carlo modeled MTF.

Detectors that have broadband response from the visible (∼ 400 nm) to near infrared (∼ 2.5 μm) have remote sensing hyper spectral applications on a single chip. Cut-off wavelengths in the 2.2 and 2.5 μm range permit detector operation in the 200 K regime. The DRS HDVIP detector technology is a front side illuminated detector technology. Consequently, there is no substrate to absorb the visible photons as in backside-illuminated detectors and these 2.2 and 2.5-μm-cutoff detectors should be well suited to respond to visible light. However, HDVIP detectors are passivated using CdTe that absorbs the visible light photons. CdTe with a direct bandgap ∼ 1.6 eV strongly absorbs photons of wavelength shorter than about 800 nm. Detectors in 320 x 6 arrays with varying thickness of CdTe passivation layers were fabricated to investigate the visible response of the 2.5-μm-cutoff detectors. The SWIR HDVIP detectors have well known high quantum efficiency (QE) in the near infrared region. The focus here was in acquiring array level data in the visible region of the spectrum. The 320 x 6 FPA QE and NEI data were acquired using a 642 nm narrow band filter with 50 % points at 612 nm and 698 nm. The array QE average is ∼ 70 % for the array with CdTe passivation thickness = 44.5 nm. The NEI is ∼ 5 x 10 10 ph/cm 2 /s at a flux Φ = 5.36 x 10 13 ph/cm 2 /s. QE for an array with CdTe passivation thickness = 44.5 nm is ∼ 10 % higher than an array with CdTe passivation thickness = 79.3 nm. In addition, a model that takes into account the complex optical properties of every layer in the HDVIP photodiode architecture was developed to predict the QE of the detectors in the near infrared and visible wavelength regions as a function of CdTe thickness. Measured QE as a function of wavelength is not a good match to the model QE probably due to limitations in the measured QE and knowledge of optical constants that are input into the model.

To protect maritime sovereignty, security forces require real-time information concerning the location, identification and activity of ships operating within their 200 nautical mile Exclusive Economic Zone (EEZ). Today, monitoring of surface activity within the EEZ is limited and largely dependent on co-operative vessels voluntarily communicating their intentions to local shore-side authorities as well as on those vessel sightings reported by patrollers. Recent advances in technology provide maritime nations with options to provide more systematic surveillance of both cooperative and noncooperative targets. This paper presents a network-centric approach to maintaining a dynamic picture of surface activity within the EEZ. The system is characterised by the use of land-based High Frequency Surface Wave Radar (HFSWR) to provide persistent surveillance of all ocean-going vessels. However, translating this track information into actionable data requires that as many of the tracks as possible are tagged with their corresponding vessel identification. In this paper we introduce space-based interception of a vessel's Automated Identification Systems (AIS) broadcast to provide the identification and location of appropriately equipped vessels. In such a system those radar tracks not associated with an appropriate AIS (or, for that matter, AIS tracks where there is no supporting sensor data), can be highlighted for priority attention.

DRS LPE-grown SWIR, MWIR and LWIR HgCdTe material are fabricated in the High-Density Vertically Integrated Photodiode (HDVIP) architecture. Instruments manufactured for certain strategic applications have severe constraints on excess low frequency noise due to the effect the noise has on the image quality with subsequent consequences on the period of calibration. This paper will present data and analysis of excess low frequency noise in LWIR (lc ~ 10.5 mm @ 60 K) HDVIP HgCdTe detectors. The vehicle for noise measurements is a multiplexed 320 x 6 array of 40 mm x 50 mm, 10.5 mm cutoff, HgCdTe detectors. Noise has been measured on a column of 320 detectors, at 60 K, as a function of frequency at zero and 50 mV reverse bias. Integration time for the measurement was 1.76 ms. Output voltage for the detectors was sampled every 10th or every 100th frame. 32,768 frames of time series data were collected for a total record length of 98 minutes. Since the total time for collecting the 32,768 time data series points is 98 minutes, the minimum frequency is 170 mHz. Time series and Fourier transform data on individual detectors at 0 mV and 50 mV reverse bias in the dark have been studied. Examination of the detector current time series and Fourier transform curves thereof, reveal a variety of interesting characteristics: (i) time series displaying switching between four states characteristic of random telegraph signal (RTS) noise, the noise current power spectrum having Lorentzian type characteristics; (ii) time series data exhibiting slight wave-like characteristics with the noise current power spectrum being 1/f-like at low frequencies; (iii) pronounced wave-like characteristics in the time series with the noise current power spectrum being 1/f2-like at low frequencies; and (iv) time series having a mean value independent of time with the noise current power spectrum being white. The predominance of detectors examined had minimal excess low frequency noise down to ~ 10 mHz. In addition some isolated diodes had characteristics that lay between the four main types outlined above.

In this work, we develop a mercury-cadmium-telluride linear array detection system that is capable of rapidly capturing (∼1-5 s) a broad spectrum of atomic and molecular laser-induced breakdown spectroscopy (LIBS) emissions in the long-wave infrared (LWIR) region (∼5.6-10 μm). Similar to the conventional UV-Vis LIBS, a broadband emission spectrum of condensed phase samples covering the whole 5.6-10 μm region can be acquired from just a single laser-induced microplasma or averaging a few single laser-induced microplasmas. Atomic and molecular signature emission spectra of solid inorganic and organic tablets and thin liquid films deposited on a rough asphalt surface are observed. This setup is capable of rapidly probing samples "as is" without the need of elaborate sample preparation and also offers the possibility of a simultaneous UV-Vis and LWIR LIBS measurement.

DRS uses LPE-grown SWIR, MWIR and LWIR HgCdTe material to fabricate High-Density Vertically Integrated Photodiode (HDVIP) architecture detectors. 2.5 μm, 5.3 μm and 10.5 μm cutoff detectors have been fabricated into linear arrays as technology demonstrations targeting remote sensing programs. This paper presents 320 x 6 array configuration technology demonstrations' performance of HDVIP HgCdTe detectors and single detector noise data. The single detector data are acquired from within the 320 x 6 array. Within the arrays, the detector size is 40 μm x 50 μm. The MWIR detector array has a mean quantum efficiency of 89.2% with a standard deviation to mean ratio, σ/μ = 1.51%. The integration time for the focal plane array (FPA) measurements is 1.76 ms with a frame rate of 557.7 Hz. Operability values exceeding 99.5% have been obtained. The LWIR arrays measured at 60 K had high operability with only ~ 3% of the detectors having out of family response. Using the best detector select (BDS) feature in the read out integrated circuit (ROIC), a feature that picks out the best detector in every row of six detectors, a 320 x 1 array with 100% operability is obtained. For the 320 x 1 array constituted using the BDS feature, a 100% operable LWIR array with average NEI value of 1.94 x 1011 ph/cm 2/s at a flux of 7.0 x 1014 ph/cm2/s has been demonstrated. Noise was measured at 60 K and 50 mV reverse bias on a column of 320 diodes from a 320 x 6 LWIR array. Integration time for the measurement was 1.76 ms. Output voltage for the detectors was sampled every 100th frame. 32,768 frames of time series data were collected for a total record length of 98 minutes. The frame average for a number of detectors was subtracted from each detector to correct for temperature drift and any common-mode noise. The corrected time series data was Fourier transformed to obtain the noise spectral density as a function of frequency. Since the total time for collecting the 32,768 time data series points is 98.0 minutes, the minimum frequency is 170 μHz. A least squares fit of the form (A/f + B) is made to the noise spectral density data to extract coefficients A and B that relate to the 1/f and white noise of the detector respectively. In addition noise measurements were also acquired on columns of SWIR detectors. Measurements were made under illuminated conditions at 4 mV and 50 mV reverse bias and under dark conditions at 50 mV reverse bias. The total collection time for the SWIR detectors was 47.7 minutes. The detectors are white noise limited down to ~10 mHz under dark conditions and down to ~ 100 mHz under illuminated conditions.

Remote sensing programs require detectors with a variety of wavelengths. One example of remote sensing applications is the GOES-ABI program that requires linear arrays of detectors with cutoff wavelengths ranging from the visible to the VLWIR (λc ~ 15 μm). In order to target the variety of remote sensing applications, an internal task was conducted to develop detectors and linear arrays operating under nominal remote sensing applications. SWIR [λc(295 K) ~ 2.5 μm] test detectors have been measured as a function of temperature between 170 K and 295 K. At 200 K the RoA values are in the 106 ohm-cm2 range. MWIR [λc(60 K) = 5.3 μm] and LWIR [λc(60 K) = 10.5 μm] HgCdTe detectors in a 320 x 6 array format have also been measured at 60 K. Within the arrays, the detector size is 40 μm x 50 μm. The MWIR detector array has a mean quantum efficiency of 89.2 % with a standard deviation to mean ratio, σ/μ = 1.51 %. The integration time for the focal plane array (FPA) measurements is 1.76 ms with a frame rate of 557.7 Hz. Operability values exceeding 99.5 % have been obtained. In addition, test diodes at the edge of the array that did not go through a read out integrated circuit (ROIC) were also measured and had quantum efficiency ~ 86 % that agreed well with the ~ 87 % quantum efficiency measured for detectors in the array that were located near the test detectors. The LWIR arrays, measured at 60K also had high operability with only ~ 3 % of the detectors having out of family response. Using best detector select (BDS) feature in the read out integrated circuit (ROIC), a feature that picks out the best detector in every row of six detectors, a 320 x 1 array with 100 % operability is obtained. For the 320 x1 array constituted using the BDS feature, a 100 % operable LWIR array with average NEI value of 1.94x1011 ph/cm2/s at a flux of 7.0x1014 ph/cm2/s has been demonstrated.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS), is overseen by the Integrated Program Office (IPO), a joint effort of the Department of Defense, Department of Commerce and NASA. One of the instruments on the NPOESS satellite is the Cross-track Infrared Sounder (CrIS) instrument. CrIS is a Fourier Transform interferometric infrared (FTIR) sensor used to measure earth radiance at high spectral resolution to derive pressure, temperature, and moisture profiles of the atmosphere from the ground on up. Each CrIS instrument contains three different cutoff wavelength (λc)focal plane modules (FPMs): an SWIR FPM [λc(98 K) ~ 5 mm], MWIR FPM [λc(98 K) ~ 9 mm] and a LWIR FPM [λc(81 K) ~ 15.5 mm]. There are nine large (850 mm diameter) photodiodes per FPM, the nine detectors being arranged in a 3 x 3 array. The nine detectors are placed under tight tolerances in the X, Y, and Z dimensions. The steps involved in the transfer of photodiodes as part of a newly fabricated wafer to the mounting of the photodiodes on the FPM involves many processing steps including a significant amount of dicing, cleaning, wire bonding and baking at elevated temperatures. Quantum efficiency and 1/f noise in Hg1-xCdxTe photodiodes are critical parameters that limit the sensitivity of infrared sounders. The ratio α, defined as the noise current in unit bandwidth in(f = 1 Hz, Vd, Δf = 1 Hz) to the dark current Id(Vd), that is, α = in/Id is one of the parameters used to select photodiodes for placement in FPMs. α is equivalent to √αH/N that appears in the well-known Hooge expression. For the sixty-one, λc ~ 9 μm photodiodes measured at 60 mV reverse bias and at 98 K, the average value of αdark = 1.3 x 10-4 in the dark and αPHOTO = in/IPHOTO is ~ 2 x 10-6 under illuminated conditions. These values of α are a factor of two lower than that reported previously. The λc ~ 15.5 μm photodiodes have average αdark = 1.3 x 10-5 with the highest performance, diffusion current limited photodiodes having values of αdark in the mid 10-6 range. All of the 850 μm diameter, λc ~ 15.5 μm photodiodes measured have excess low frequency noise, with the best performers having in(f = 100 Hz, Vd =-60 mV , Δf = 1 Hz) ~ 2 x 10-11 A/Hz1/2 and the best photodiode αdark = 3.92 x 10-6. I-V measurements, noise, and visual inspections are performed at several steps in the photodiodes manufacturing process. It was observed, following FPM fabrication, photodiode dark current and noise had increased from the initial pre-mounting leadless chip carrier (LCC) measurements for some of the nine photodiodes. The performance degradation observed led to an investigation into the cause (baking at elevated temperatures, mechanical handling, electrical stress etc.) of photodiode degradation that occurred between LCC and FPM testing. Correlations between I-V, noise and surface visual defects have been performed on some λc ~ 15.5 mm photodiodes. This paper outlines the results of the study, correlating the electrical performance observed to visual defects on the surface and to defects seen following cross sectioning of degraded photodiodes. In addition, other lessons learned and the corrective actions implemented that led to the successful manufacture of SWIR, MWIR and LWIR large photodiodes from the material growth to insertion into and successful demonstration of flight FPMs for the CrIS program are described.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Cross-track Infrared Sounder (CrIS), an interferometric sounder, is one of the instruments within the National Polar-orbiting Operational Environmental Satellite System (NPOESS) suite. CrIS measures earth radiances at high spectral resolution providing accurate and high-resolution pressure, temperature and moisture profiles of the atmosphere. These profiles are used in weather prediction models to track storms, predict levels of precipitation etc. Each CrIS instrument contains three Focal Plane Array Assemblies (FPAAs): SWIR [λ c (98 K) ~ 5 mm], MWIR [λ c (98 K) ~ 9 mm], and LWIR [λ c (81 K) ~ 16 mm]. Each FPAA consists of nine large (850-mm-diameter) photovoltaic detectors arranged in a 3 x 3 pattern, with each detector having an accompanying cold preamplifier. This paper describes the selection methodology of the detectors that constitute the FPAAs and the performance of the CrIS SWIR, MWIR and LWIR proto-flight FPAAs. The appropriate bandgap n-type Hg 1-x Cd x Te was grown on lattice-matched CdZnTe. 850-mm-diameter photodiodes were manufactured using a Lateral Collection Diode (LCD) architecture. Custom pre-amplifiers were designed and built to interface with these large photodiodes. The LWIR, MWIR and SWIR detectors are operated at 81 K, 98 K and 98 K respectively. These relatively high operating temperatures permit the use of passive radiators on the instrument to cool the detectors. Performance goals are D* = 5.0 x 10 10 cm-Hz 1/2 /W at 14.0 mm, 9.3 x 10 10 cm-Hz 1/2 /W at 8.0 mm and 3.0 x 10 11 cm-Hz 1/2 /W at 4.64 mm. Measured mean values for the nine photodiodes in each of the LWIR, MWIR and SWIR FPAAs are D* = 5.3 x 10 10 cm-Hz 1/2 /W at 14.0 mm, 1.0 x 10 11 cm-Hz 1/2 /W at 8.0 mm and 3.1 x 10 11 cm-Hz 1/2 /W at 4.64 mm. These compare favorably with the following BLIP D* values calculated at the nominal flux condition: D* = 8.36 x 10 10 cm Hz 1/2 /W at 14.0 mm, 1.4 x 10 11 cm-Hz 1/2 /W at 8.0 mm and 4.1 x 10 11 cm-Hz 1/2 /W at 4.64 mm.

Detector characteristics of Au- and Cu-doped High Density Vertically Integrated Photodiode (HDVIP) detectors are presented in this paper. Individual photodiodes in test bars were examined by measuring I-V curves under dark and illuminated conditions at high bias values. Noise as a function of frequency has been measured on Au- and Cu-doped MWIR [λ c (78 K) = 5 μ] HDVIP HgCdTe diodes at several temperatures under dark and illuminated conditions. No excess currents are observed above the photocurrents for reverse bias values out to 500 mV. Both Au- and Cu-doped detectors measured at 85 K, exhibit gain values between 40 and 50 at 8 V reverse bias. Gain values fell in this same range even when the flux incident on each type of detector was varied. The excess noise factor for the Cu-doped detectors ranged from 1.35 to 1.69 depending on the incident flux. Variation is probably due to measurement error. The noise at 8 V reverse bias is white for the Cu-doped detectors. The Au-doped detectors exhibited 1/f noise at 8 V reverse bias. At higher frequencies where the noise spectrum was quasi-white, the excess noise factor for the Au-doped detector was in the 1.0 to 1.5 range.

Cu-doped HDVIP ® detectors with different cut-off wavelengths are routinely manufactured. The DRS HDVIP ® detector technology is a front-side-illuminated detector technology. There is no substrate to absorb the visible photonsas in backside-illuminated detectors and these detectors should be well suited to respond to visible light. However,HDVIP ® detectors are passivated using CdTe that absorbs the visible light photons. CdTe strongly absorbs photons ofwavelength shorter than about 800 nm. Detectors with varying thickness of CdTe passivation layers were fabricated toinvestigate the visible response of the 2.5- µ m-cutoff detectors. A model was developed to predict the quantumefficiency of the detectors in the near infrared and visible wavelength regions as a function of CdTe thickness.Individual photodiodes ( c =2.5µ m) in test bars were examined. Measurements of the quantum efficiency as afunction of wavelength region will be presented and compared to the model predictions.Keywords: infrared, HDVIP

Photon detectors and focal plane arrays (FPAs) are fabricated from HgCdTe and silicon in many varieties. With appropriate choices for bandgap in HgCdTe, detector architecture, dopants, and operating temperature, HgCdTe and silicon can cover the spectral range from ultraviolet to the very-long-wavelength infrared (VLWIR), exhibit high internal gain to allow photon counting over this broad spectral range, and can be made in large array formats for imaging. DRS makes HgCdTe and silicon detectors and FPAs with unique architectures for a variety of applications. Detector characteristics of High Density Vertically Integrated Photodiode (HDVIP) HdCdTe detectors as well as Focal Plane Arrays (FPAs) are presented in this paper. MWIR[λc(78 K) = 5 μm] HDVIP detectors RoA performance was measured to within a factor or two or three of theoretical. In addition, 256 x 256 detector arrays were fabricated. Initial measurements had seven out of ten FPAs having operabilities greater than 99.45% with the best 256 x 256 array having only two inoperable pixels. LWIR [λc(78K)~10 μm] 640 X 480 arrays and a variety of single color linear arrays have also been fabricated. In addition, two-color arrays have been fabricated. DRS has explored HgCdTe avalanche photo diodes (APDs) in the λc = 2.2 μm to 5 μm range. The λc = 5 μm APDs have greater than 200 DC gain values at 8 Volts bias. Large-format to 10242 Arsenic-doped (Si:As, λc ~ 28 μm), Blocked-Impurity-Band (BIB) detectors have been developed for a variety of pixel formats and have been optimized for low, moderate, and high infrared backgrounds. Antimony-doped silicon (Si:Sb) BIB arrays having response to wavelengths > 40 μm have also been demonstrated. Avalanche processes in Si:As at low temperatures (~ 8 K) have led to two unique solid-state photon-counting detectors adapted to infrared and visible wavelengths. The infrared device is the solid-state photomultiplier (SSPM). A related device optimized for the visible spectral region is the visible-light photon counter (VLPC). The VLPC is a nearly ideal device for detection of small bunches of photons with excellent time resolution. Finally, DRS makes imaging arrays of pin-diodes utilizing the intrinsic silicon photoresponse to provide high performance over the 0.4-1.0 μm spectral range operating near room temperature. pin-diode arrays are particularly attractive as an alternative to charge-coupled devices (CCDs) for space applications where radiation hardening is needed. In addition, wire grid micropolarizers have been demonstrated and two color doped silicon detectors using diffractive microlenses are being developed. Precision alignment of sensor chips with respect to a base mounting plate has been demonstrated to be within 2 μm. A similar technique is also utilized to align single large detectors for sounder applications in focal plane arrays (FPAs). FPAs for space applications with the associated cold and warm electronics and packaging/cables have been fabricated.

Photon detectors and focal plane arrays (FPAs) are fabricated from silicon in many varieties. With appropriate choices for detector architecture, dopants, and operating temperature, silicon can cover the spectral range from ultraviolet to the very-long-wavelength infrared (VLWIR), exhibit high internal gain to allow photon counting over this broad spectral range, and can be made in large array formats for imaging. DRS makes silicon detectors and FPAs with unique architectures for a variety of applications. Large-format, VLWIR FPAs based on doped-silicon Blocked-Impurity-Band (BIB) detectors have been developed. These FPAs comprise an array of BIB detectors interfaced via indium column interconnects to a matching read-out integrated circuit (ROIC). Arsenic-doped silicon (Si:As) BIB detector arrays with useful photon response out to about 28 μm are the most fully developed embodiment of this technology. FPAs with Si:As BIB arrays have been made in a variety of pixel formats (to 1024 2 ) and have been optimized for low, moderate, and high infrared backgrounds. Antimony-doped silicon (Si:Sb) BIB arrays having response to wavelengths 40 μm have also been demonstrated. Avalanche processes in Si:As at low temperatures (~ 8 K) have led to two unique solid-state photon-counting detectors adapted to infrared and visible wavelengths. The infrared device is the solid-state photomultiplier (SSPM). To our knowledge, it is the only detector capable of counting VLWIR photons (formula available in paper) with high quantum efficiency. A related device optimized for the visible spectral region is the visible-light photon counter (VLPC). The VLPC is a nearly ideal device for detection of small bunches of photons with excellent time resolution. VLPCs coupled to scintillating fibers have demonstrated new capabilities for energetic charged particle tracking in high-energy physics. A fiber tracking system that utilizes VLPCs is currently in operation in the D0 detector at Fermilab's Tevatron. VLPCs may also be useful for quantum cryptography and quantum computation. Finally, DRS makes imaging arrays of pin -diodes utilizing the intrinsic silicon photoresponse to provide high performance over the 0.4 - 1.0 μm spectral range operating near room temperature. pin -diode arrays are particularly attractive as an alternative to charge-coupled devices (CCDs) for space applications where radiation hardening is needed.

Detector characteristics of Cu- and Au-doped High Density Vertically Integrated Photodiode (HDVIP) detectors as well as Cu-doped HDVIP Focal Plane Arrays (FPAs) are presented in this paper. Individual photodiodes in test bars were examined by measuring I-V curves and the associated resistance-area (RA) product as a function of temperature. The Au-doped MWIR [λ c (78 K) = 5 μm] HDVIP detectors RoA performance was within a factor of two or three of theoretical. Noise as a function of frequency has been measured on Au-doped MWIR HgCdTe HDVIP diodes at several temperatures under dark and illuminated conditions. Low-frequency noise performance of the Au-doped MWIR diode in the various environments is characterized by the ratio α of the noise current spectral density at 1 Hz to the value of the diode current. For photocurrent at 140 K, α PHOTO = 1.8 x 10 -5 . The value of α PHOTO is the same at both zero bias and 100 mV reverse bias. At 160 K, α PHOTO is slightly lower but still in the low 10 -5 range. Excess low-frequency noise measured at 140 K and 100 mV reverse bias in the dark has α DARK = 1.4 x 10 -5 . At 160 K and 100 mV reverse bias, α DARK is in the mid 10 -5 range. At 140 K,the dark current at 8.2 V reverse bias was equal to the photocurrent at 100 mV reverse bias and close to the photocurrent at zero bias. α DARK = 1.85 x 10 -3 at -8.2 V. This ratio is two orders of magnitude greater than α PHOTO . At 8.2 V reverse bias, the current was amplified by avalanche processes. Similar results were obtained on the Au-doped diode at 160 K. Diffusion current dominates dark current at 100 mV reverse bias at T = 185 K and T = 220 K. The ratio, α DARK approximately α PHOTO in the low to mid 10 -5 range, i.e. dark diffusion current generates excess low frequency noise in the same manner as photocurrent. In addition, 256 x 256 Cu-doped detector arrays were fabricated. Initial measurements had seven out of ten FPAs having operabilities greater than 99.45% with the best 256 x 256 array having only two inoperable pixels.

The effect of radiation on HgCdTe photodiodes is an important parameter to understand when determining the long-term performance limitations for the Cross-track Infrared Sounder (CrIS), a Fourier Transform interferometric sensor that will fly as part of the National Polar-orbiting Operational Environmental Satellite System (NPOESS). The CrIS sensor uses relatively large area photovoltaic detectors, 1 mm in diameter. Each p-on-n HgCdTe photodiode consists of MBE grown, n-type material on lattice matched CdZnTe, with arsenic implantation used to form the junction. A 1mm diameter detector is achieved by using a lateral collection architecture. Solar, and trapped protons are a significant source of radiation in the NPOESS 833 km orbits. We irradiated 22 LWIR detectors with protons at the Harvard Cyclotron Laboratory (HCL) and monitored the I-V performance and dynamic impedance of each detector. Three groups of detectors were irradiated with either 44, 99, or 153-MeV protons, each between 1×1010 - 4×1012 p+/cm2. Several I-V data sets were collected within that fluence range at all three energies. All the detectors were warmed to room temperature for approximately 96 hours following the largest proton dose, re-cooled, and then re-characterized in terms of I-V performance and dynamic impedance. The total noise increase predicted for CrIS after 7-years in orbit is less than 1%.

Short wavelength, middle wavelength, mid-long wavelength, long wavelength, and very long wavelength focal plane arrays (FPAs) are required for remote sensing applications. Advances in the Molecular Beam Epitaxy (MBE) growth of Mercury Cadmium Telluride (HgCdTe) and detector architectures utilized, have resulted in high performance detectors being fabricated in the 1 micrometers to 16 micrometers spectral range Custom Read Out Integrated Circuits (ROICs) are designed and fabricated to interface the HgCdTe detector arrays. The hybrid focal pane array is made up of the HgCdTe detector array and the CMOS-based ROIC. Hybrid FPAs performance parameters are presented. The HgCdTe detector material is used are grown by MBE on lattice matched CdZnTe substrates. Custom ROICs are fabricated in a commercial CMOS foundry. FPA D* performance values have been obtained for a multitude of spectral ranges and configurations that include; (i) (lambda) c equals 1.8 micrometers , 12 X 256 arrays operating at 295 K with median D* approximately 1.4 X 1012 cm Hz1/2/W, (ii) (lambda) c equals 10.5 micrometers , 256 X 256 arrays operating at 85 K with medina D* equals 3.9 X 1011 cm Hz1/2/W at a background flux (phi) b equals 7.82 X 1015 ph/cm2-2 and (iii) (lambda) c equals 15.8 micrometers at 65K, 128 X 128 array operating at 40K with peak D* of 2.76 X 1011 cm Hz1/2/W at a background flux (phi) b equals 8.0 X 1015 ph/cm2- s. The performance of these FPAs will be presented.

Infrared (IR) remote sensing imaging applications require high-performance Focal Plane Arrays (FPAs) operating in all ranges of the IR spectrum. Short wavelength (SWIR; 1 to 3 micrometer), middle wavelength (MWIR; 3 to 5 micrometer), mid- long wavelength (MLWIR; 6 to 8 micrometer), long wavelength (LWIR; 8 to 14 micrometer), and very long wavelength (VLWIR; greater than 14 micrometer). These diverse spectral bands require high performance detectors and Read Out Integrated Circuits (ROICs) to perform the multi-spectral mission requirements. Significant progress in the design and fabrication of HgCdTe detector arrays and Read Out Integrated Circuits (ROICs) over the past few years has led to the demonstration of high resolution, low noise and large format reliable FPAs. Hybrid FPAs have been measured and their performance parameters are presented. Focal Plane Array D* performance values have been obtained for a multitude of spectral ranges and configurations that include; (1) (lambda) c equals 1.8 micrometer, 12 X 256 arrays operating at 295 K with median D* approximately 1.4 X 1012 cm Hz1/2/W, (2) (lambda) c equals 2.4 micrometer, 12 X 256 arrays operating at 250 K with median D* equals 1.6 X 1012 cm Hz1/2/W, detectors used are grown by MBE on lattice matched CdZnTe, (3) PACE-1 detectors with (lambda) c equals 2.5 micrometer, 1024 X 1024 arrays operating at 115 K with peak D* of 2.3 X 1013 cm Hz1/2/W at a background flux (phi) b equals 1.2 X 1011 ph/cm2- s, (4) MBE HgCdTe on Silicon MWIR detectors have been fabricated and the detector RoA performance for (lambda) co approximately 5.0 micrometer is in the 106 to 107 ohm-cm2 range at 78 K. (5) MBE HgCdTe on CdZnTe detectors, ((lambda) c equals 15.8 micrometer at 65 K), 128 X 128 array operating at 40 K with peak D* of 2.76 X 1011 cm Hz1/2/W at a background flux (phi) b equals 8.0 X 1015 ph/cm2-s. High performance 640 X 480 arrays imaging in the MWIR band have been fabricated on CdZnTe and PACE-1 substrates. The performance of these and additional FPAs will be presented.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical quantum communication utilizing satellite platforms has the potential to extend the reach of quantum key distribution (QKD) from terrestrial limits of ~200 km to global scales. We have developed a thorough numerical simulation using realistic simulated orbits and incorporating the effects of pointing error, diffraction, atmosphere and telescope design, to obtain estimates of the loss and background noise which a satellite-based system would experience. Combining with quantum optics simulations of sources and detection, we determine the length of secure key for QKD, as well as entanglement visibility and achievable distances for fundamental experiments. We analyze the performance of a low Earth orbit (LEO) satellite for downlink and uplink scenarios of the quantum optical signals. We argue that the advantages of locating the quantum source on the ground justify a greater scientific interest in an uplink as compared to a downlink. An uplink with a ground transmitter of at least 25 cm diameter and a 30 cm receiver telescope on the satellite could be used to successfully perform QKD multiple times per week with either an entangled photon source or with a weak coherent pulse source, as well as perform long-distance Bell tests and quantum teleportation. Our model helps to resolve important design considerations such as operating wavelength, type and specifications of sources and detectors, telescope designs, specific orbits and ground station locations, in view of anticipated overall system performance.