We have previously discussed the potential of using a Hg1-xCdxTe source as a reference plane for the non-uniformity
correction of thermal imagers and which is being developed as an option for the UK 3rd generation, high performance
thermal imaging program (Albion). In this paper we will present our first results on a large area (1.5 cm x 1.5 cm) source
which was grown on a silicon substrate and can simulate a range of temperatures from -10 °C to +30 °C. Due to the fast
switching speed, the apparent temperature can be changed on a frame by frame basis. Also, the operation of the device
can be synchronized to the integration time of the camera to reduce the mean power requirements by a factor of 10 and
reduce thermal heating effects. The main applications for Hg1-xCdxTe devices as high-performance, cryogenically-cooled
detectors typically require very low drive currents. The use of this material for large-area LEDs has generated new
challenges to deal with the high peak currents. These are typically in the range 1-2 A/cm2 for a MWIR waveband source
and have led to a need to reduce the common impedance, reduce the contact resistances and consider the effects of
Negative luminescent (NL) devices, which to an IR observer can appear colder than they actually are, have a wide range of possible applications, including use as modulated IR sources in gas sensing systems and as thermal radiation shields in IR cameras. A further important use would be a calibration source for IR focal plane arrays where there are many potential advantages over conventional sources, including high speed operation (for multi-point correction) and lower power consumption. Such applications present considerable technological challenges as they require large area uniform devices (>1cm2) with a large apparent temperature range.
In this paper we report on recent progress in fabricating large area (1.5cm × 1.5cm) negative luminescence devices from Hg1-xCdxTe grown on silicon substrates using a segmented device architecture.
Negative luminescent devices, which absorb more light than they emit when reverse biased, have a large number of applications including, reference planes for thermal cameras, infrared (IR) sources and IR scene projection. This paper describes devices made from mercury cadmium telluride grown on silicon substrates, focusing on large area arrays with reduced operating powers. Novel growth structures and device designs have been investigated in order to reduce the series resistance. Results from the first dry etched, LW MCT on Si, 1 cm2 device with optical concentrators are presented.
Dual-waveband, Focal Plane Arrays (FPAs) based on Hg1-xCdxTe multi-layer structures have previously been produced by the Molecular Beam Epitaxy (MBE) growth technique. It is shown that the multi-layer structures required for dual-waveband devices can also be grown by Metal Organic Vapor Phase Epitaxy (MOVPE). The MOVPE growth process allows excellent control of both the composition and doping profiles and has the advantage of allowing growth on a range of substrates including silicon. Previous research on back-to-back diodes for dual-waveband has concentrated on npn structures. The design of the alternative pnp structures is discussed and a model is developed which gives a good fit to the measured spectra. We report on the design and characterization of dual-waveband detectors including current-voltage and spectral cross talk for the case of two close sub-bands within the 3-5 μm mid-wave infrared (MWIR) spectral range. The mechanisms for spectral cross talk are discussed including incomplete absorption, transistor action and radiative coupling. A custom readout circuit (ROIC) has been designed. This allows the capture of data from the two bands which is spatially aligned but sequential in time.