ESTO Investments in Innovative Sensor Technologies for Remote Sensing

For more then 18 years NASA Earth Science Technology Office has been investing in remote sensing technologies. During this period ESTO has invested in more then 900 tasks. These tasks are managed under multiple programs like Instrument Incubator Program (IIP), Advanced Component Technology (ACT), Advanced Information Systems Technology (AIST), In-Space Validation of Earth Science Technologies (InVEST), Sustainable Land Imaging - Technology (SLI-T) and others. This covers the whole spectrum of technologies from component to full up satellite in space and software. Over the years many of these technologies have been infused into space missions like Aquarius, SMAP, CYGNSS, SWOT, TEMPO and others. Over the years ESTO is actively investing in Infrared sensor technologies for space applications. Recent investments have been for SLI-T and InVEST program. On these tasks technology development is from simple Bolometers to Advanced Photonic waveguide based spectrometers. Some of the details on these missions and technologies will be presented

Blocking contacts for N-type cadmium zinc telluride

A process for applying blocking contacts on an n-type CdZnTe specimen includes cleaning the CdZnTe specimen; etching the CdZnTe specimen; chemically surface treating the CdZnTe specimen; and depositing blocking metal on at least one of a cathode surface and an anode surface of the CdZnTe specimen

GaN/AlGaN Avalanche Photodiode Detectors for High Performance Ultraviolet Sensing Applications

The shorter wavelengths of the ultraviolet (UV) band enable detectors to operate with increased spatial resolution, variable pixel sizes, and large format arrays, benefitting a variety of NASA, defense, and commercial applications. AlxGa1-xN semiconductor alloys, which have attracted much interest for detection in the UV spectral region, have been shown to enable high optical gains, high sensitivities with the potential for single photon detection, and low dark current performance in ultraviolet avalanche photodiodes (UV-APDs). We are developing GaN/AlGaN UV-APDs with large pixel sizes that demonstrate consistent and uniform device performance and operation. These UV-APDs are fabricated through high quality metal organic chemical vapor deposition (MOCVD) growth on lattice-matched, low dislocation density GaN substrates with optimized material growth and doping parameters. The use of these low defect density substrates is a critical element to realizing highly sensitive UV-APDs and arrays with suppressed dark current under high electric fields.Optical gains greater than 5X10 (exp 6) with enhanced quantum efficiencies over the 350-400 nm spectral range have been demonstrated, enabled by a strong avalanche multiplication process. Furthermore, we are developing 6X6 arrays of devices to test high gain UV-APD array performance at ~355 nm. These variable-area GaN/AlGaN UV-APD detectors and arrays enable advanced sensing performance over UV bands of interest with high resolution detection for NASA Earth Science applications

Development of High-Performance Graphene-HgCdTe Detector Technology for Mid-Wave Infrared Applications

A high-performance graphene-based HgCdTe detector technology is being developed for sensing over the mid-wave infrared (MWIR) band for NASA Earth Science, defense, and commercial applications. This technology involves the integration of graphene into HgCdTe photodetectors that combines the best of both materials and allows for higher MWIR(2-5 m) detection performance compared to photodetectors using only HgCdTe material. The interfacial barrier between the HgCdTe-based absorber and the graphene layer reduces recombination of photogenerated carriers in the detector. The graphene layer also acts as high mobility channel that whisks away carriers before they recombine, further enhancing the detector performance. Likewise, HgCdTe has shown promise for the development of MWIR detectors with improvements in carrier mobility and lifetime. The room temperature operational capability of HgCdTe-based detectors and arrays can help minimize size, weight, power and cost for MWIR sensing applications such as remote sensing and earth observation, e.g., in smaller satellite platforms. The objective of this work is to demonstrate graphene-based HgCdTe room temperature MWIR detectors and arrays through modeling, material development, and device optimization. The primary driver for this technology development is the enablement of a scalable, low cost, low power, and small footprint infrared technology component that offers high performance, while opening doors for new earth observation measurement capabilities

Development of High Performance Detector Technology for UV and Near IR Applications

Sensing and imaging for ultraviolet (UV) and nearinfrared (NIR) bands has many applications forNASA, defense, and commercial systems. Recentwork has involved developing UV avalanchephotodiode (UV-APD) arrays with high gain for highresolution imaging. Various GaN/AlGaN p-i-n (PIN)UV-APDs have been fabricated from epitaxialstructures grown by MOCVD on GaN substrates withavalanche gains higher than 5 x 10(exp 5), and significantlyhigher responsivities. Likewise, the SiGe materialsystem allows the demonstration of high-performancedetector array technology that covers the 0.5 to 1.7 mwavelength range for visible and NIR bands ofinterest. We have utilized SiGe fabrication technologyto develop Ge based PIN detector devices on 300 mmSi wafers. We will discuss the theoretical andexperimental results from electrical and opticalcharacterization of the detector devices with variousn+ region doping concentrations to demonstrate low dark currents below 1 uA at -1 V and high photocurrent. Recent results from these detectorarrays for UV and NIR detection will be presented

The 12x32 Pop-Up Bolometer Array for the SHARC II Camera

SHARC II is a 350 micron facility camera for the Caltech Submillimeter Observatory (CSO) expected to come on-line in 2002. The key component of SHARC II is a 12x32 array of doped silicon 'pop-up' bolometers developed at NASA/Goddard and delivered to Caltech in March 2002. Each pixel is 1 mm x 1 mm, coated with a 400 Omega/square bismuth film, and located lambda/4 above a reflective backshort to maximize radiation absorption. The pixels cover the focal plane with greater than 95% filling factor. Each doped thermistor occupies nearly the full area of the pixel to minimize 1/f noise. We report some results from the first cold measurements of this array. The bolometers were located inside a dark cover, and 4x32 pixels were read simultaneously. In the best 25% of winter nights on Mauna Kea, SHARC II is expected to have an NEFD at 350 microns of 1 Jy s(sup 1/2) or better

Design and Fabrication of Two-Dimensional Semiconducting Bolometer Arrays for the High Resolution Airborne Wideband Camera (HAWC) and the Submillimeter High Angular Resolution Camera II (SHARC-II)

The High resolution Airborne Wideband Camera (HAWC) and the Submillimeter High Angular Resolution Camera II (SHARC 11) will use almost identical versions of an ion-implanted silicon bolometer array developed at the National Aeronautics and Space Administration's Goddard Space Flight Center (GSFC). The GSFC "Pop-Up" Detectors (PUD's) use a unique folding technique to enable a 12 x 32-element close-packed array of bolometers with a filling factor greater than 95 percent. A kinematic Kevlar(Registered Trademark) suspension system isolates the 200 mK bolometers from the helium bath temperature, and GSFC - developed silicon bridge chips make electrical connection to the bolometers, while maintaining thermal isolation. The JFET preamps operate at 120 K. Providing good thermal heat sinking for these, and keeping their conduction and radiation from reaching the nearby bolometers, is one of the principal design challenges encountered. Another interesting challenge is the preparation of the silicon bolometers. They are manufactured in 32-element, planar rows using Micro Electro Mechanical Systems (MEMS) semiconductor etching techniques, and then cut and folded onto a ceramic bar. Optical alignment using specialized jigs ensures their uniformity and correct placement. The rows are then stacked to create the 12 x 32-element array. Engineering results from the first light run of SHARC II at the CalTech Submillimeter Observatory (CSO) are presented