Heterostructure infrared photovoltaic detectors

HgCdTe remains the most important material for infrared (IR) photodetectors despite numerous attempts to replace it with alternative materials such as closely related mercury alloys (HgZnTe, HgMnTe), Schottky barriers on sili con, SiGe heterojunctions, GaAs/AlGaAs multiple quantum wells, InAs/GaInSb strained layer superlattices, high temperature superconductors and especial ly two types of thermal detectors: pyroelectric detectors and silicon bolom eters. It is interesting, however, that none of these competitors can compe te in terms of fundamental properties. In addition, HgCdTe exhibits nearly constant lattice parameter which is of extreme importance for new devices b ased on complex heterostructures. The development of sophisticated controll able vapour phase epitaxial growth methods, such as MBE and MOCVD, has allo wed fabrication of almost ideally designed heterojunction photodiodes. In t his paper, examples of novel devices based on heterostructures operating in the long wavelength, middle wavelength and short wavelength spectral range s are presented. Recently, more interest has been focused on pn junction he terostructures. As infrared technology continues to advance, there is a gro wing demand for multispectral detectors for advanced IR systems with better target discrimination and identification. HgCdTe heterojunction detectors offer wavelength flexibility from medium wavelength to very long wavelength and multicolour capability in these regions. Recent progress in two-colour HgCdTe detectors is also reviewed. (C) 2000 Elsevier Science B.V. All righ ts reserved.