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Intracellular transport along cytoskeletal filaments propelled by molecular motors ensures the targeted delivery of cargoes to their destinations. Such transport is rarely unidirectional but rather bidirectional, including intermittent pauses and directional reversals owing to the simultaneous presence of opposite-polarity motors. It has been unclear whether such a complex motility pattern results from the sole mechanical interplay between opposite-polarity motors or requires external regulators. Here, we addressed this outstanding question by reconstituting cargo motility along microtubules in vitro by attaching purified Dynein-Dynactin-BICD2 (DDB) and kinesin-3 (KIF16B) to large unilamellar vesicles. Strikingly, we found that this minimal system is sufficient to recapitulate runs, pauses and reversals similar to in vivo cargo motility. In our experiments, reversals were always preceded by vesicle pausing and the transport directionality could be tuned by the relative numbers of opposite-polarity motors on the vesicles. Unexpectedly, during all runs the vesicle velocity was not influenced by the presence of the opposing motors. To gain mechanistic insight into bidirectional transport, we developed a mathematical model which predicts that low numbers of engaged motors are critical to transition between runs and pauses. Taken together, our results suggest that motors diffusively anchored to membranous cargo transiently engage in a tug-of-war during pauses where stochastic motor attachment and detachment events can lead to directional reversals without the necessity of external regulators.

Honeywell Aerospace is implementing on behalf of the Canadian Space Agency the Quantum Encryption and Science Satellite (QEYSSat), a Canadian-owned and operated scientific and technology demonstration mission aimed at developing the next-generation of secure communications infrastructure backed by quantum physics. The mission management is led by the Canadian Space Agency and the science is led by the Institute for Quantum Computing at the University of Waterloo. Quantum key distribution (QKD) is a method for issuing, via single-photon transmission, verifiably-confidential encryption keys between two parties. This capability is a powerful tool for the transfer of sensitive data (e.g. financial transactions, health records, etc.), however current terrestrial QKD networks are limited to a few hundred kilometres in geographic reach between nodes. The QEYSSat mission will use a satellite receiver as a trusted node to demonstrate the distribution of secure keys between ground stations separated by at least 400 km. In addition, Honeywell intends to fly an optical intersatellite link (OISL) terminal as a hosted payload on this mission. The QEYSSat mission will utilize both weak coherent pulse (WCP) sources and entangled photon sources in an uplink configuration to study the performance of QKD, and to perform Bell tests of long-range quantum entanglement. Honeywell is building the QKD receiver terminal consisting of a front-end telescope, a precision pointing and tracking system and single-photon detectors. Major technical challenges include polarization management throughout the optical chain, accurate pointing and tracking, and suppression of background and stray light sources. To address these challenges, Honeywell is leveraging its existing commercial optical communications solutions to meet the more stringent performance requirements for space-based QKD. The QKD terminal architecture consists of an afocal front-end telescope, a wide FOV high-precision pointing and tracking assembly, a polarization analyzer and single-photon photodetector system. A large-diameter on-axis telescope for geostationary optical communications forms the basis for the terminal’s front-end optics, and Honeywell’s commercial Optical Pointing and Tracking Relay Assembly for intersatellite Communications (OPTRAC) has been adapted as a quantum-ready pointing and tracking unit (QTRAC). For each element, substantial effort has been made to develop an optical system that preserves single-photon states with high fidelity despite the large number of optical surfaces in the chain. The optical assembly for the QKD terminal was developed and tested at the breadboard level in 2020; this paper will highlight the development and testing of these units as well as the overall architecture and concept of the QEYSSat mission.

Secure optical communications networks are a functional requirement for many military, government, and civilian applications. Optical free space links provide security due to the small ground footprint of highly collimated laser beam patterns. Space-based optical communications provide an additional layer of security due to dynamic angular tracking requirements and remote orbiting infrastructure. The addition of Quantum Key Distribution (QKD) adds a third layer of safety through the use of physically unbreakable keys. The QEYSSat mission is scheduled to launch in 2022. This mission will carry a primary QKD science payload and a secondary high-speed optical communications demonstration payload. The QEYSSat secondary communications payload (QP2) is the latest space-based optical communications terminal designed to be amenable to low cost mass production methods, meeting the price targets of many planned low-earth-orbit optical communications constellations. The successful demonstration of both technologies on a single micro-satellite platform demonstrates the key technologies necessary to enable next generation high speed secure communications networks. In this paper we present an overview of the QEYSSAT optical payloads and describe secure architectures for QKD-enabled optical communications network applications.

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

Honeywell Aerospace has been selected by the Canadian Space Agency to implement the Quantum Encryption and Science Satellite (QEYSSat), a Canadian-owned and operated scientific and technology demonstration mission towards the next-generation of secure communications infrastructure. Quantum key distribution (QKD) is a method for distributing, via single-photon transfer, verifiably-confidential encryption keys between two parties separated by large distances. This capability is a powerful tool for the transmission of sensitive data (e.g. financial transactions, personal health records, etc.), however current ground-based QKD networks are limited in geographic reach to roughly 200 kilometres. The QEYSSat mission will use a satellite receiver to demonstrate the distribution of secure keys between ground stations separated by at least 400 km. In addition, Honeywell intends to fly an optical intersatellite link (OISL) terminal as a hosted payload on this mission. The QEYSSat mission will implement both weak coherent pulse (WCP) sources and entangled photon sources to study the performance of QKD, and to perform Bell tests of long-range quantum entanglement. Honeywell is building the free-space QKD terminal consisting of a large-diameter front-end telescope, a precision pointing and tracking system, single-photon receiver, and a downlink source. Major technical challenges include accurate pointing and tracking, polarization-management throughout the optical chain, and deep suppression of background and stray light sources, given the nature of single photon exchange over large distances. To address these challenges, Honeywell is leveraging its existing optical communications solutions to meet the enhanced performance requirements for space-based QKD. A large-format telescope for geostationary optical communications forms the basis for the terminal's front-end optics, and Honeywell's commercially-focused Optical Pointing and Tracking Relay Assembly for intersatellite Communications (OPTRAC) is being adapted as a high-performance, quantum-ready pointing and tracking unit (QTRAC). This paper discusses the design of the QKD terminal and will highlight results from the recently completed QEYSSat Phase A study.

Canada has vast water resources that span an enormous range in geography, climate, and ecosystems [1]. Water supply and water quality are the two critical issues relevant to water resources, not only in Canada but globally in a warming climate. The water microsatellite mission described here aims to better prepare end users to respond to the emerging spectrum of water futures issues by revolutionizing remote sensing of water quality and quantity parameters, and permitting unprecedented interconnection and data gathering from Canadian environmental monitoring networks.

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.

Type-II strained-layer superlattices (T2SLs) are receiving increased interest as mid-wave infrared (MWIR) and long-wave infrared detector absorbers due to their potential Auger suppression and ability to be integrated into complex device structures. Although T2SLs show promise for use as infrared detectors, further investigation into the effects of high energy particle radiation is necessary for space-based applications. In this presentation, the effects of both 4.5 MeV and 63 MeV proton radiation on the carrier lifetime of MWIR InAs/InAsSb T2SLs will be shown. The 63 MeV proton radiation study will focus on the carrier lifetime of MWIR InAs/InAsSb T2SL samples of varying donor density. These results reveal a Shockley-Read-Hall (SRH) lifetime associated with a radiation induced defect level, which is not dependent on the donor density of the T2SL. Using 4.5 MeV proton radiation, the dependence of carrier lifetime on relative trap density in MWIR T2SLs samples is studied by varying the particle fluence. A comparison of these two radiation studies shows similar lifetime effects that will be discussed in detail. These results give insight into the viability of Ga-free T2SLs for space applications.

Aims In the present study, to investigate its chemical stability and the in vitro sun protection factor (SPF) of Rosa kordesii petal extract in a gel formulation. Methods Due to its antioxidant and photoprotective properties, R. kordesii is a promising candidate for use in cosmetic and pharmaceutical formulations. A high performance liquid chromatography method was used to evaluate the chemical stability using R. kordesii extract as marker at 5, 25 and 45 °C for 3–4 months. The sun protection factors were analyzed by ultraviolet (UV) spectrophotometry using samples irradiated with UVB lamp. Results The chemical stability of the R. kordesii root extract gel was determined according to the concentration of R. kordesii extracts at different storage temperatures (5, 25 and 45 °C) for 3–4 months. It is screened for in vitro sun protection factor in the R. kordesii extract and of its gel formulation and determines Photostability of the isolated R. kordesii extract and SPF. Conclusion This study has shown that the R. kordesii petal extract gel is stable for at least 3–4 months when stored at 5 and 25 °C. It is essential for collection of similar data for different plants and their flowers, as well as other parts. This proved activity of plant showed its importance and prophylactic utility in anti-solar formulation. This will be a better, cheaper and safe alternative to harmful chemical sunscreens that used now a days in the industry.

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.

InAs1−x Sb x material with an alloy composition of the absorber layer adjusted to achieve 200-K cutoff wavelengths in the 5-μm range has been grown. Compound-barrier (CB) detectors were fabricated and tested for optical response, and J dark–V d measurements were taken as a function of temperature. Based on absorption coefficient information in the literature and spectral response measurements of the midwave infrared (MWIR) nCBn detectors, an absorption coefficient formula α(E, x, T) is proposed. Since the presently suggested absorption coefficient is based on limited data, additional measurements of material and detectors with different x values and as a function of temperature should refine the absorption coefficient, providing more accurate parametrization. Material electronic structures were computed using a k·p formalism. From the band structure, dark-current density (J dark) as a function of bias (V d) and temperature (T) was calculated and matched to J dark–V d curves at fixed T and J dark–T curves at constant V d. There is a good match between simulation and data over a wide range of bias, but discrepancies that are not presently understood exist near zero bias.

The COM DEV Mission Development Group has recently launched a nanosatellite mission called NTS (Nanosatellite Tracking of Ships). NTS is a space trial, intended to provide proof-of-concept validation for a COM DEV AIS (Automatic Identification System) radio that has been specifically designed to receive ship AIS transmissions from low Earth orbit. The AIS system uses the very high frequency (VHF) band and provides detailed information about each equipped vessel. Not only does this system provide information such as the location of a vessel, but it also provides heading, engine status and other crucial information about the ship. Designed for terrestrial use, the AIS system traditionally has a range of only 100 km and uses a local self-organized time-division multiple access (SO-TDMA) scheme to ensure transmissions from all ships in any self-organized cell do not overlap. Receiving these signals from a space platform presents an opportunity to provide wide area monitoring of shipping activity. Detection of AIS signals from space will provide a new capability to track and monitor large maritime vessels even when there are large distances from traditional shore based detection systems. The NTS program was designed to be a low cost demonstration satellite and provide rapid risk mitigation to assist in the development of a future constellation of spacecraft that could provide operational AIS from space (AIS-S) reception and dissemination. The scope of the NTS program was kept to a minimum with focus on the design, development and demonstration of a new payload. The nanosatellite bus was developed using a combination of pre-existing designs by the University of Toronto Institute of Aerospace Studies/Space Flight Laboratory (UTIAS/SFL). The resulting bus design was a combination of their CanX-2 and Generic Nanosatellite Bus. The NTS spacecraft is able to provide the capability to detect AIS signals from low earth orbit with multiple, short AIS signal collection cycles over its planned mission lifetime. The paper presents an overview of the NTS spacecraft, mission concept and preliminary results obtained from the flight.

Increasing very long-wave infrared (VLWIR, λ c ≈ 15 μm) pixel operability was approached by subdividing each pixel into four interdigitated subpixels. High response is maintained across the pixel, even if one or two interdigitated subpixels are deselected (turned off), because interdigitation provides that the preponderance of minority carriers photogenerated in the pixel are collected by the selected subpixels. Monte Carlo modeling of the photoresponse of the interdigitated subpixel simulates minority-carrier diffusion from carrier creation to recombination. Each carrier generated at an appropriately weighted random location is assigned an exponentially distributed random lifetime τ i, where 〈τ i〉 is the bulk minority-carrier lifetime. The minority carrier is allowed to diffuse for a short time dτ, and the fate of the carrier is decided from its present position and the boundary conditions, i.e., whether the carrier is absorbed in a junction, recombined at a surface, reflected from a surface, or recombined in the bulk because it lived for its designated lifetime. If nothing happens, the process is then repeated until one of the boundary conditions is attained. The next step is to go on to the next carrier and repeat the procedure for all the launches of minority carriers. For each minority carrier launched, the original location and boundary condition at fatality are recorded. An example of the results from Monte Carlo modeling is that, for a 20-μm diffusion length, the calculated quantum efficiency (QE) changed from 85% with no subpixels deselected, to 78% with one subpixel deselected, 67% with two subpixels deselected, and 48% with three subpixels deselected. Demonstration of the interdigitated pixel concept and verification of the Monte Carlo modeling utilized λ c(60 K) ≈ 15 μm HgCdTe pixels in a 96 × 96 array format. The measured collection efficiency for one, two, and three subelements selected, divided by the collection efficiency for all four subelements selected, matched that calculated using Monte Carlo modeling.

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.

We demonstrated a device with a unique planar architecture using a novel approach for obtaining low arsenic doping concentrations in long-wavelength (LW) HgCdTe on CdZnTe substrates. HgCdTe materials were grown by molecular beam epitaxy (MBE). We fabricated a p-on-n structure that we term P +/π/N + where the symbol “π” is to indicate a drastically reduced extrinsic p-type carrier concentration (on the order of mid 1015 cm−3); P + and N + denote a higher doping density, as well as a higher energy gap, than the photosensitive base π-region. Fabricated devices indicated that Auger suppression is seen in the P +/π/N + architecture at temperatures above 130 K and we obtained a saturation current on the order of 3 mA on 250-μm-diameter devices at 300 K with Auger suppression. Data shows that about a 50% reduction in dark current is achieved at 300 K due to Auger suppression. The onset of Auger suppression voltage is 450 mV at 300 K and 100 mV at 130 K. Results indicate that a reduction of the series resistance could reduce this further. A principal challenge was to obtain low p-type doping levels in the π-region. This issue was overcome using a novel deep diffusion process, thereby demonstrating successfully low-doped p-type HgCdTe in MBE-grown material. Near-classical spectral responses were obtained at 250 K and at 100 K with cut-off wavelengths of 7.4 μm and 10.4 μm, respectively. At 100 K, the measured non-antireflection-coated quantum efficiency was 0.57 at 0.1 V under backside illumination.

Time series and Fourier-transform data on high-density vertically integrated photodiodes (HDVIP) at 0 and 50 mV reverse bias in the dark have been studied. The detectors have a cutoff wavelength λc (60 K) of 10.5 μm. Examination of the detector current time series and Fourier-transform curves of these devices reveals 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 or double Lorentzian type characteristics, (ii) time series data exhibiting wave-like characteristics with the noise current power spectrum being 1/f2-like at low frequencies, (iii) time series having a mean value independent of time with the noise current power spectrum being white, and (iv) time series nearly independent of time with the noise current power spectrum having 1/f characteristics. Although from a single array, the excess noise characteristics at low (mHz) frequencies were varied, most of the detectors measured fell into one of these four categories. The predominance of detectors examined had minimal excess low-frequency noise down to ~ 10 mHz. Detectors that displayed RTS noise in reverse bias were repeatable under subsequent measurement. However, when measured at zero bias, the same detectors exhibited no RTS noise, the noise current power spectrum being white in nature.

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.

State-of-the-art large-area photovoltaic (PV) detectors fabricated in HgCdTe grown by molecular beam epitaxy (MBE) have been demonstrated for the Crosstrack Infrared Sounder (CrIS) instrument. Large-area devices (1 mm in diameter) yielded excellent electrical and optical performance operating at 81 K for λc ∼ 15 µm, at 98 K for λc ∼ 9 µm, and λc ∼ 5-µm spectral cutoffs. Fabricated detectors have near-theoretical electrical performance, and Anti Reflection coated quantum efficiency (QE) is greater than 0.70. Measured average RoA at 98 K is 2.0E7 Ωcm2, and near-theoretical QEs greater than 0.90 were obtained on detectors with λc ∼ 5-µm spectral cutoffs. These state-of-the-art large-area PV detector results reflect high-quality HgCdTe grown by MBE on CdZnTe substrates in all three spectral bands of interest.

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.

The Institute for Telecommunications Research (ITR) at the University of South Australia has led a consortium, including COM DEV International, to design a low Earth orbit microsatellite constellation mission with a customized communications systems architecture, using specialized waveform designs to create a Global Sensor Network (GSN). The GSN provides a low-cost mechanism for gathering data from a very large number of remote land and marine sensors in the field of view of the satellite, and delivering information to end users. The system allows users to control and upgrade their remotely deployed devices, if necessary. One of the principal requirements of the GSN is that it be able to handle up to 100,000 sensor-terminals during a ten minute satellite pass. This is accomplished by novel waveforms and high-efficiency communication protocols resulting in a flexible and scalable satellite system that communicates with large numbers of terminals using low bandwidth. The techniques have been successfully validated in airborne and limited satellite trials using existing space assets and a bent-pipe system to demonstrate proof of concept. A key differentiator between the GSN and existing constellations such as Iridium, Globalstar etc., is that the low cost is achieved by recognizing that large classes of sensors don't necessarily require continuous access to a satellite, and only need to transmit short burst data at relatively long intervals. Populating the planet with sensors of all types expands the concept of the "internet of things" to remote locations such as the polar caps, the oceans, and remote forests and deserts, and can potentially tie together diverse datasets for natural resource management, security, research and environmental monitoring Refereed/Peer-reviewed

In this era Bacteria are mostly considered as pathogenic. Bacteria though are pathogenic but still a few are friendly and essential for human growth and immunity; called as Probiotics. Lactobacillus model moiety is one of such probiotic bacterium which when introduced in sufficient colony serves as new prophylaxis and curing agent. This will increase the innate immunity of humans. Indian market lacks the quality uni-strain product of the probiotics as Nutraceuticals and as Health enhancing drug product. Global market is full of multi-strain microbes dosage form. The best mode to utilize Nutraceutical aspect of probiotics is to convert in dry form. These purified colony; later converted into the solid dry form by spray dry (JISL mini-spray drier) technique. Starch, lactose were used as thermo-protective agent while heat drying technique. Anti-microbial screenings carried out along with In vitro cytotoxicity studies. In vitro cytotoxicity screening evaluated that Lactobacillus powder showings anti-cancer activity nearly same as standard drug with no side effects. Dry powder increased the shelf life of the microbes that resulted in maintenance of viability and activity.

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.

Satellites offer the means to extend quantum communication and quantum key distribution towards global distances. We will outline the proposed QEYSSat mission proposal, which involves a quantum receiver onboard a satellite that measures quantum signals sent up from the ground. We present recent studies on the expected performance for quantum links from ground to space. Further studies include the demonstration of high-loss quantum transmission, and analyzing the effects of a fluctuating optical link on quantum signals and how these fluctuations can actually be exploited to improve the link performance.

Participation in physical activity can improve the health outcomes of breast cancer survivors. To impact public health, broad-reaching sustainable interventions that promote physical activity are needed.To evaluate the efficacy of two distance-based interventions for promoting physical activity among breast cancer survivors compared with a standard recommendation control.Breast cancer survivors who had finished 'active' cancer treatment were eligible to participate. Participants (n = 330) were randomly assigned to receive one of the following mail-delivered interventions: three computer-tailored newsletters, a previously developed breast cancer-specific physical activity booklet or a pamphlet detailing the public health recommendations for physical activity (control). Primary outcomes were self-reported moderate to vigorous aerobic activity and participant's self-reported resistance training activity at 4 months post-baseline. Secondary outcomes were pedometer step counts, whether or not participants were meeting the physical activity guidelines, time spent in sedentary behaviour, fatigue and health-related quality of life.Participants randomised into the tailored-print intervention group were three times more likely to commence resistance training and meet the resistance-training guidelines immediately after the intervention than participants allocated to the control group. There were no other significant intervention effects.Computer-tailored newsletters may be an effective strategy for enhancing resistance-based physical activity among breast cancer survivors. The null findings relating to other outcomes may be due to ceiling effects (in the case of aerobic activity, fatigue and health-related quality of life) or the sensitivity of the measure used (in the case of sitting time). These issues require further exploration.

Very long wavelength infrared (VLWIR; 15 to 17 µm) detectors are required for remote sensing sounding applications. Infrared sounders provide temperature, pressure and moisture profiles of the atmosphere used in weather prediction models that track storms, predict levels of precipitation etc. Traditionally, photoconductive VLWIR (λc >15 µm) detectors have been used for sounding applications. However, photoconductive detectors suffer from performance issues, such as non-linearity that is 10X – 100X that of photovoltaic detectors. Radiometric calibration for remote sensing interferometry requires detectors with low non-linearity. Photoconductive detectors also suffer from non-uniform spatial optical response. Advances in molecular beam epitaxy (MBE) growth of mercury cadmium telluride (HgCdTe) and detector architectures have resulted in high performance detectors fabricated in the 15 µm to 17 µmm spectral range. Recently, VLWIR (λc ∼ 17 µm at 78 K) photovoltaic large (1000 µm diameter) detectors have been fabricated and measured at flux values targeting remote sensing interferometry applications. The operating temperature is near 78 K, permitting the use of passive radiators in spacecraft to cool the detectors. Detector non-AR coated quantum efficiency >60% was measured in these large detectors. A linear response was measured, while varying the spot size incident on the 1000 µm detectors. This excellent response uniformity, measured as a function of spot size, implies that low frequency spatial response variations are absent. The 1000 µm diameter, λc ∼ 17 µm at 78 K detectors have dark currents ∼160 µA at a −100 mV bias and at 78 K. Interfacing with the low (comparable to the contact and series resistance) junction impedance detectors is not feasible. Therefore a custom pre-amplifier was designed to interface with the large VLWIR detectors operating in reverse bias. A breadboard was fabricated incorporating the custom designed preamplifier interfacing with the 1000 µm diameter VLWIR detectors. Response versus flux measurements were made on the large VLWIR detectors and non-linearity

Long wavelength infrared molecular beam epitaxy (MBE) grown p-on-n Hg1−xCdxTe double layer planar heterostructure (DLPH) detectors have been characterized to determine the dominant mechanisms limiting their performance. Material defects have been identified as critical factors that limit 40K performance operability. This effort has concentrated on identifying microscopic defects, etch pit density (EPD) and relating these defects to the device performance. Visual inspection indicates defect densities as high as 105 per cm2 with a spatial extent as observed by atomic force microscope in the range of micrometers extending several micrometers beneath the surface. At high EPD values (greater than low 106 cm−2) zero bias resistance (R0) at 40K decreases as roughly as the square of the EPD. At 78K, however, measured R0 is not affected by the EPD up to densities as high as mid-106 cm−2. Visual defects greater than 2–3 µm than ∼2 µm in size (micro-void defects) result in either a single etch pit or a cluster of etch pits. Large variations in a cross-wafer etch pit distribution are most likely a major contributor to the observed large spreads in 40K R0. This study gives some insight to the present limitation to achieve higher performance and high operability for low temperature infrared applications on MBE grown HgCdTe material.

Excess low frequency noise is investigated for the first time in infrared MBE grown LWIR Hg1−xCdxTe double layer planar heterostructure (DLPH) detectors grown on lattice matched substrates. LWIR detectors having R0Aopt values at 40K in the 101–107 Θ-cm2 range have been characterized as a function of temperature between 120 and 20K. Detectors with R0Aopt≥103Θ-cm2 at 40K have theoretical diffusion limited performance down to 78K and detectors with R0Aopt ≥105 Θ-cm2 at 40K are within a factor of two of theoretical diffusion limited performance for T>65K. Activation energies extracted from noise (Vd=−100 mV) and dark current (Vd=−100 mV) vs temperature measurements were detector dependent. The activation energy for detectors with R0Aopt≈106 Θ-cm2 at 40K is ∼0.90*Eg to 0.99*Eg. The noise measured between 78 and 105K in the intermediate performance (R0Aopt∼103–104 Θ-cm2 at 40K) detectors are higher than the noise measured in the higher performance (R0Aopt∼105–107 Θ-cm2) detectors. In addition, the excess low frequency noise and the dark current at −100 mV in the intermediate and poor (R0Aopt∼101 Θ-cm2) performance detectors are temperature independent. For each detector measured, the activation energy extracted from noise (Vd=−100 mV) vs temperature measurements is equal to the activation energy extracted from the total dark current (Vd=−100 mV) vs temperature measurements. For different dark current mechanisms, the excess low frequency noise varies with temperature and also with area within statistical accuracy in the same manner as the total dark current through the detector. At 78K, the Tobin14 expression holds in the general sense for equal area detectors dominated by different current mechanisms and also for detectors with a wide range of implant dimensions (Aimp=3.85×10−7 cm2 to Aimp=6.25×10−4 cm2). Following measurements, the detectors were stripped of the passivation and overlaying metal layers and dressed by a defect etch to reveal defects in each detector. A correlation among noise, leakage current and defect type has been determined for each detector.

The model used in this calculation is based on the model of Kalman and Tran. That model, which uses fewer parameters than any other model, successfully reproduces the spectroscopy and decay rates of baryons in the uds sector. It is not as good in the b and c sectors, because it uses a fixed value of α s . In this model the value of α is taken as the experimental value at the Z mass and the values at all other scales are obtained using the renormalization group applied to quasi particles within the baryon. These quasi particles are excitations of the three—body baryon system which behave as two—body systems. Excellent agreement with experiment is achieved. Since an iterative procedure exists that aligns the model with that of Kalman and Tran in the uds sectors, this model is consistent over the entire baryon spectra.

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.

The molecular beam epitaxy (MBE) growth technology is inherently flexible in its ability to change the Hg1−xCdxTe material’s bandgap within a growth run and from growth run to growth run. This bandgap engineering flexibility permits tailoring the device architecture to the various specific requirements. Material with active layer x values ranging from ∼0.198 to 0.570 have been grown and processed into detectors. This wide range in x values is perfectly suited for remote sensing applications, specifically the National Polar Orbiting Environmental Satellite System (NPOESS) program that requires imaging in a multitude of infrared spectral bands, ranging from the 1.58 to 1.64 µm VSWIR (very short wave infrared) band to the 11.5 to 12.5 µm LWIR (longwave infrared) band and beyond. These diverse spectral bands require high performance detectors, operating at two temperatures; detectors for the VSWIR band operate near room temperature while the SWIR, MWIR (mid wave infra red), LWIR and VLWIR (very long wave infrared) detectors operate near 100K, because of constraints imposed by the cooler for the NPOESS program. This paper uses material parameters to calculate theoretical detector performance for a range of x values. This theoretical detector performance is compared with median measured detector optical and electrical data. Measured detector optical and electrical data, combined with noise model estimates of ROIC performance are used to calculate signal to noise ratio (SNR), for each spectral band. The SNR are compared with respect to the meteorological NPOESS system derived focal plane. The derived system focal plane requirements for NPOESS are met in all the spectral bands.

Short wave infrared (SWIR) devices have been fabricated using Rockwell’s double layer planar heterostructure (DLPH) architecture with arsenic-ion implanted junctions. Molecular beam epitaxially grown HgCdTe/CdZnTe multilayer structures allowed the thin, tailored device geometries (typical active layer thickness was ∼3.5 µm and cap layer thickness was ∼0.4 µm) to be grown. A planar-mesa geometry that preserved the passivation advantages of the DLPH structure with enhanced optical collection improved the performance. Test detectors showed Band 7 detectors performing near the radiative limit (∼3-5X below theory). Band 5 detector performance was ∼4-50X lower than radiative limited performance, apparently due to Shockley-Hall-Read recombination. We have fabricated SWIR HgCdTe 256 × 12 × 2 arrays of 45 um × 45 µm detector on 45 µm × 60 µm centers and with cutoff wavelength which allows coverage of the Landsat Band 5 (1.5−1.75 µm) and Landsat Band 7 (2.08−2.35 µm) spectral regions. The hybridizable arrays have four subarrays, each having a different detector architecture. One of the Band 7 hybrids has demonstrated performance approaching the radiative theoretical limit for temperatures from 250 to 295K, consistent with test results. D* performance at 250K of the best subarray was high, with an operability of ∼99% at 1012 cm Hz1/2/W at a few mV bias. We have observed 1/f noise below 8E-17 AHz 1/2 at 1 Hz. Also for Band 7 test structures, Ge thin film diffractive microlenses fabricated directly on the back side of the CdZnTe substrate showed the ability to increase the effective collection area of small (nominally

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.

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.

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.

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.

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 .