Research on Mercury Cadmium Telluride (HgCdTe or MCT) and group III-V based infrared materials is being conducted for the development of advanced, especially large area IR detector and focal plane arrays. The focus of this research has been on materials for Quantum Well Infrared Photo Detectors (QWIPs), Sb based type II superlattice detectors, Silicon based substrates for MCT detectors and MCT detectors with higher operating temperature. Recently research has been initiated in dilute Nitride materials.
To improve the quantum efficiency, reproducibility and operating temperature of the QWIP detectors, a corrugated design has been implemented. For superlattice detectors, focal plane arrays for the MWIR spectral band have been successfully demonstrated and good image quality has been obtained. Current efforts are concentrated on achieving high quality materials and passivation techniques for the LWIR spectral band. A recently initiated effort on dilute Nitride materials holds the premise to obtain high quality direct bandgap detectors with III-V materials. For MCT detectors on Si based substrates MWIR detectors have been demonstrated with high quality, but for LWIR detector arrays of sufficient low defect densities have not been obtained on a consistent basis. Recent efforts showing promising results will be discussed.
We report on results of laboratory and field tests of dual- band MWIR/LWIR focal plane arrays (FPAs) produced under the Army Research Laboratory's Multidomain Smart Sensor Federated Laboratory program. The FPAs were made by DRS Infrared Technologies using the HgCdTe material system and by BAE Systems using QWIP technology. The HgCdTe array used the DRS HDVIP<SUP>TM</SUP> process to bond two single-color detector structures to a 640 X 480-pixel single-color read-out integrated circuit (ROIC) to produce a dual-band 320 X 240 pixel array. The MWIR and LWIR pixels are co-located and have a high fill factor. The images from each band may be read out either sequentially (alternating frames) or simultaneously. The alternating frame approach must be used to produce optimal imagery in both bands under normal background conditions. The QWIP FPA was produced using MBE-grown III-V materials. The LWIR section consisted of GaAs quantum wells and AlGaAs barriers and the MWIR section used InGaAs quantum wells with AlGaAs barriers. The detector arrays were processed with three ohmic contacts for each pixel allowing for independent bias control over both the MWIR and LWIR sections. The arrays were indium bump-bonded to an ROIC (specifically designed for two color operation) which puts out the imagery from both bands simultaneously. The ROIC has variable gain and windowing capabilities. Both FPAs were tested under similar ambient conditions with similar optical components. The FPAs were subjected to a standard series of laboratory performance tests. The relative advantages and disadvantages of the two material systems for producing medium-format dual-band FPAs are discussed.
The Army Research Laboratory (ARL) conducts a broad-based optoelectronics R and D program that addresses a number of Army applications. This program covers the full range of activities from basic materials development to component development and integration into higher levels of optoelectronic functionality. This paper addresses technology areas of interest to ARL including IR detection and imaging, IR sources, ladar, multifunction optoelectronic integration, diffractive optics, optoelectronic interconnects/processing, waveguide integrated optics, wide bandgap optoelectronics, and nonlinear optics. These areas represent a cross-section of the work conducted in the Sensors and Electron Deices Directorate of ARL. Space does not allow comprehensive discussion of the R and D program each of these technology thrust ares, but references are provided in each case so that the interested reader can pursue each of these topics further.
The multi-domain smart sensor (MDSS) program combines research efforts of an industry/university consortium and the Army Research Laboratory (ARL). The consortium is headed by Lockheed Martin; other members are DRS, the University of New Mexico, Stanford University, and the Massachusetts Institute of Technology. This paper describes the concept and the current status of research and development of the MDSS program. The goal of this program is to develop technologies that will allow significant improvements in situation awareness and target detection and identification, especially of low observable targets. A notional system concept has been developed that guides the research. Under this concept, improved target detection will be obtained by passive imaging with large-area, dual-color IR focal plane arrays (IRFPA) operating in the mid-wave (MWIR) and the long-wave (LWIR) spectral bands. Once target detection is achieved, target identification - if necessary - can be obtained through active imaging with a noval, scannerless ladar system. To materialize this concept, research and development is performed for dual-color IRFPAs, and an eyesafe laser and a demodulator for the returning radiation - both required to operate up the MHz frequencies. Also, hyperspectral imaging is investigated for detection of camouflaged targets. In support of this effort, field measurements have been performed with boresighted MWIR and LWIR cameras to obtain pixel registered imagery for the development of effective fusion and processing algorithms.
Infrared sensor technology is critical to many commercial and military defense applications. Traditionally, cooled infrared material systems such as indium antimonide, platinum silicide, mercury cadmium telluride, and arsenic doped silicon (Si:As) have dominated infrared detection. Improvement in surveillance sensors and interceptor seekers requires large size, highly uniform, and multicolor IR focal plane arrays involving medium wave, long wave, and very long wave IR regions. Among the competing technologies are the quantum well infrared photodetectors based on lattice matched or strained III-V material systems. This paper discusses cooled IR technology with emphasis on QWIP and MCT. Details will be given concerning device physics, material growth, device fabrication, device performance, and cost effectiveness for LWIR, VLWIR, and multicolor focal plane array applications.
Over the past several years, uncooled IR detectors and focal plane arrays have been rapidly developed. Impressive progress has been made in both resistive microbolometers and pyroelectric thin-film detectors with noise equivalent temperature differences projected to be 10 to 20 mK with F/1 optics for such structures. Noise equivalent temperature of 50 mK bulk pyroelectric detectors and thin film resistive microbolometers are already demonstrated and in production. Other novel schemes, such as bimaterial capacitors, are also promising for uncooled IR detection. The US Army Research Laboratory is involved in developing ferroelectric materials to take advantage of the pyroelectric properties. The goal is to develop crystal oriented thin films to further improve detector performance. In this presentation, the operating principle of resistive microbolometers and pyroelectric detectors, and recent progress of uncooled RI focal plane arrays are discussed. In addition, the uncooled RI detector program at the Army Research Laboratory, that includes research facilities for and research efforts toward uncooled detectors and focal plane arrays is presented.