Assessment of HgCdTe photodiodes and quantum well infrared photoconductorsfor long wavelength focal plane arrays

Recent trends in infrared detectors are towards large, electronically addre ssed two-dimensional arrays. In the long wavelength infrared (LWIR) spectra l range HgCdTe focal plane arrays (FPAs) occupy a dominant position. Howeve r, the slow progress in the development of large LWIR photovoltaic HgCdTe i nfrared imaging arrays and the rapid achievements of novel semiconductor he terostructure systems have made it necessary to foresee the future developm ent of different material technologies in fabrication large FPAs. Among the competing technologies in LWIR are the quantum well infrared photoconducto rs (QWIPs) based on lattice matched GaAs/AlGaAs and strained layer InGaAs/A lGaAs material systems. This paper compares the technical merits of two IR detector arrays technologies; photovoltaic HgCdTe and QWIPs. It is clearly shown that LWIR QWIP cannot compete with HgCdTe photodiode as the single de vice especially at higher temperature operation (> 70 K) due to fundamental limitations associated with intersubband transitions. However, the advanta ge of HgCdTe is less distinct in temperature range below 50 K due to proble ms involved in HgCdTe material (p-type doping, Shockley-Read recombination, trap-assisted tunnelling, surface and interface instabilities). Even thoug h the QWIP is a photoconductor, several of its properties such as high impe dance, fast response time, long integration time, and low power consumption , well satisfy the requirements of fabrication of large FPAs. Due to the hi gh material quality at low temperature, QWIP has potential advantages over HgCdTe for very LWIR (VLWIR) FPA applications in terms of the array size, u niformity, yield and cost of the systems. (C) 1999 Elsevier Science B.V. Al l rights reserved.