Quantum Well Infra-Red Detectors

Abstract

Infra-red photon detectors working at wavelengths longer than about 211m normally use semiconductor materials specifically developed for this purpose such as indium antimonide or mercury cadmium telluride (MCT), whose bandgaps match the photon energy of the radiation to be detected. The MCT alloy system is the most versatile such system and can be used in detectors with cut-off wavelengths varying between at least 20 µm and 2 µm. The special purpose materials systems give the highest available infra-red detector performance. However, MCT is virtually a single use material and is difficult to use because of its chemical and physical properties. The quantum well infra-red photoconductor (QWIP) is a device concept that allows general purpose electronic materials systems (e.g., GaAs/AIGaAs or Si/SiGe) to be used as infra-red detectors. These materials are highly developed for purposes such as transistors, lasers and integrated circuits and have much more attractive materials properties than MCT. The highly developed nature of the material technology used in QWIPs means that these devices have progressed rapidly from concept [1-6] to a first realization in 1987 [7] and the demonstration of arrays of -10⁵devices [8,9] on a single chip for thermal imaging applications. The availability of large area substrates and uniform epitaxial crystal growth developed for other purposes have been particularly important in achieving this last goal.