The HgCdTe semiconductor alloy system is now firmly established as today's most widely applicable high-performance infrared detector material. This paper summarizes the status of HgCdTe infrared detector technology, with emphasis on recent developments in HgCdTe photoconductive detector technology for use in first generation thermal imaging systems.
The performance status of silicon IR detectors, including spectral response, detectivity and operational temperature for use in the 2-2.5, 3-5, and 8-14 μm principal windows of the atmosphere, was recently briefly reviewed'. Such detectors operate under high radiant background conditions imposed by exposure of the detector to the ambient radiation of the atmosphere. In this review a more detailed description of the detectors is provided. It is extended to include the properties and performance of silicon detectors for use in the low background environment of space where backgrounds may be reduced by up to nine orders of magnitude. The effects of the reduced background promote high detector sensitivities, but produce unusual characteristics which are summarized. Such detectors are currently in use in the IRAS infrared astromomy telescope now orbiting in space.
Suicide Schottky diode based infrared cameras have received wide interest recently because they are easy to manufacture, non-complex and have excellent performance. In this paper we will describe the operation of Schottky cameras, point out the physical basis of their unique properties and report on the current status of this technology.
Many of the recent advances in infrared astronomy in the 1 - 5 μm region have been the result of efforts to utilize and optimize indium antimonide (InSb) detectors for this application. This paper will briefly review the progress which has been made in obtaining 2 μm NEP values as low as 10-16w-Hz-1/2 with photovoltaic InSb. More recent efforts have concentrated on other types of InSb operation, such as CID's and CCD's, which are more suited to array formats for spectroscopic and imaging applications. Advances in the fabrication of InSb photodiodes makes possible the integration of photocurrent on the detector capacitance, with the potential of measuring infrared fluxes of a few photon/s during integration times > 1000 s.
A brief review of the early development efforts in lead salt detectors is presented. Applications and methods of fabrication of contemporary devices are also discussed. State-of-the-art detectors are characterized for their chemical, structural, and photoelectronic properties. Performance characteristics as a function of operation temperature, frequency, background energy levels, etc., are described. Radiation effects are briefly discussed. A short summary of the mechanics of photoconductivity of the lead salt films is presented. Multi-element array designs and performance characteristics of typical current operational hardware are reviewed. Design and operational limitations are identified. Advanced concepts of Integrated (Hybrid and Monolithic) Detector Arrays are also reviewed.
The construction and theory of operation of thermistor detectors is reviewed. The effects of changes in ambient temperature are discussed and measures for accommodating or compensating for these effects are presented. System conditions where thermistors would be most applicable are described and a comparison made with other thermal detectors. Equations for calculating responsivity and D* are given and the improvement resulting from immersion. Unimmersed thermistor detectors will generally have D*s in the range 1 - 3 (10)8 depending on the time constant. Immersion can increase this by a factor of 3.5.
Recently published advances in readout mechanisms for IR focal plane arrays are reviewed. Hybrid CCD multiplexer approaches, IRCCD, XY readout and SPRITE are compared. Techniques which incorporate gain reduction and DC suppression are analyzed for their potential to provide adequate dynamic range.
"Hybrid array," when related to infrared mosaics, has a different meaning than the more widely accepted definition in electronic packaging. By "hybrid array" we mean the physical and electrical mating of a two-dimensional mosaic array of detectors to a multiplexer, with individual interconnects between each detector and the corresponding input to the multiplexer, to form a focal plane array (FPA). The detector mosaic is the sensing device while the multiplexer performs a self-scanning or readout function appropriate to either a staring or time-delay-and-integration (TDI) format. The integrated signal may be stored in the detector or the multiplexer.
Metal-Insulator-Semiconductor (MIS) detectors fabricated in HgCdTe offer significant advantages for focal plane applications. These detectors perform noise free signal intearation directly in the HoCdTe, can be formed in either n- or p-type material, do not require formation of a metallurgical junction, and are easy to interface to low power signal processing integrated circuits in silicon. Furthermore, this device technology readily facilitates the formation of charge transfer devices which perform some signal processing in the HaCdTe prior to transfer of the signal to the silicon processor.
This paper will survey and review the evolution and state-of-the-art of extrinsic silicon IR focal plane array technology. Extrinsic silicon photodetectors are capable of optimum infrared detection ranging from below 2 to well above 20 micrometers. Arrays of silicon detectors have been used in focal planes for both ground- and space-based operational systems such as the highly successful Infrared Arrowing Satellite (IRAS). The special properties of these detectors when they are used in conjunction with state-of-the-art charge-coupled device (CCD) multiplexing devices will have a significant impact on all future focal plane developments. The status and futured development potential of these infrared charge-coupled devices (IRCCD's) will be discussed in this paper. The concepts for and progress made toward realizing two-dimensional mosaic focal planes integrating silicon CCD multiplexers and extrinsic silicon detector array will be reviewed. Finally, the potential and applications of silicon focal planes will be assessed.
This paper reviews Indium Antimonide Charge Injection Device (CID) Technology. These detectors consist of MIS capacitors formed on InSb wafers using integrated circuit-like processing. When biased into depletions, the capacitors form integrating detectors for use in the 3-5 μ band. Single capacitors are used to form line array sites while two coupled capacitors form sites of area arrays. Silicon scanning chips are used to address the sites and implement the readout of the signal charge. Advances in the technology permit the design of IR focal planes with large numbers of detectors. General Electric has developed line arrays with up to 512 elements and staring arrays with up to 128 x 128 elements. This paper first reviews the basic CID mechanisms and briefly describes array fabrication. This is followed by a description of InSb line arrays along with their readouts and performance. Two dimensional arrays and their readouts are presented including the 128 x 128 staring array.
Recent development of high-performance Pd2Si and PtSi Schottky-barrier IR-CCD image sensors make these monolithic focal plane arrays attractive for many SWIR and thermal imaging applications. PtSi Schottky-barrier detectors operated at 80K have quantum efficiency of several percent in the 3 to 5 μm spectral range and cut-off wavelength of about 6.0 μm. Pd2Si Schottky-barrier detectors operated between 120 and 140K have cut-off wavelength of 3.6 μm and quantum efficiency in the range of 1.0 to 8.0% in the SWIR band. High-quality thermal imaging was achieved with a 64x128-element PtSi Schottky-barrier IR-CCD imager in a TV compatible IR camera operated with 60 frames per second. This paper reviews the Schottky-barrier IR-CCD technology developed at RCA. A model for photoyield of Schottky-barrier detectors (SBDs) is reviewed and compared with experimen-tal data. The architecture and design trade-offs of the SBD IR-CCD imagers are discussed. Also included is a discussion of the quantum efficiency requirements for staring thermal imagers and the performance achievable with the Schottky-barrier IR-CCD arrays.