| Abstract: | Cadmium mercury telluride is of considerable importance as a material for the detection of IR radiation. Carrier lifetime has been studied intensively as it is the principal factor controlling detector performance. Bulk lifetime is dominated by Auger processes in the narrow bandgap material sensitive between 8 and 14 μm, while it is dominated by radiative recombination in the wider bandgap material sensitive below 5 μm. Auger processes have been studied by observing the photoconductive decay as a function of temperature. This has led to an experimental determination of the overlap integral as 0.3. A fresh calculation of radiative lifetime by the van Roosbroek-Shockley method has led to an analytic expression that agrees well with observed lifetime. Recombination at discontinuities (contacts, surfaces and flaws introduced in processing) are of importance in the photoconductive detectors. Surface recombination velocity can be reduced to low values (less than 200 cm s−1) in n-type material by obtaining an accumulated surface. The rate limiting processes are then transitions between filled surface states and holes. No such accumulation appears to occur at the contacts or lines of damage introduced in processing. As a result there is considerable recombination at these features. When lifetime is controlled by transit time effects it is called sweepout. In sweepout the dependence of ambipolar mobility on majority carrier concentration leads to novel effects. Auger lifetime is reduced in low carrier concentration samples by optical injection of carriers by the background. This effect has often been ascribed to Shockley-Read recombination. These results are being used in modelling of detector performance that reproduces most of the features seen in practical detectors. |
