<title>Quantum well infrared photoconductors in infrared detectors technology</title>

Abstract

The performance of quantum well infrared photodetectors (QWIPs) as compared to other types of semiconductor infrared (IR) detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation. From the discussion results that long wavelength QWIP cannot compete with HgCdTe photodiode as the single device especially at higher temperature operation (> 70 K) due to fundamental limitations associated with intersubband transitions. However, the advantage of HgCdTe is less distinct in temperature range below 50 K because of the problems involved in an HgCdTe material (p-type doping, Shockley-Read recombination, trap-assisted tunneling, surface and interface instabilities). Due to the limited charge storage capacity of available readout circuits, a small photoconductive gain of QWIPs improves the noise equivalent difference temperature the sensor. The imaging performance of HgCdTe photodiodes and QWIP focal plane arrays can be said to be nearly equivalent when they are operated under their optimum conditions. Decision of the best technology is therefore driven by the specific needs of a system.