Infrared Absorption Behavior in CdZnTe Substrates
Authors: Sen, S.; Rhiger, D.R.; Curtis, C.R.; Kalisher, M.H.; Hettich, H.L.; Currie, M.C.
Source: Journal of Electronic Materials, Volume 30, Number 6, 1 June 2001 , pp. 611-618(8)
Abstract:Infrared (IR) optical transmission measurements of polished CdZnTe wafers can provide useful information about excess impurities, stoichiometry, and inhomogeneities (precipitates and inclusions). We have investigated the IR transmission behavior of Cd0.96Zn0.04Te between 8 m and 20 m at room temperature. The measurements were made before and after thermal treatments involving control of the Cd and Zn overpressures, which served to minimize the Cd (cation) vacancy population. Our results support the polar optical phonon scattering theory of Jensen, according to which the absorption in donor dominated CdZnTe varies as m with m = 3. For material dominated by acceptors, we show that the theoretical absorption by inter-valence band transitions can be approximated by a similar power law with exponent m = 1, and that Cd-vacancy dominated wafers are in reasonable agreement with this. We find some wafers in which the as grown condition exhibits partial compensation of impurity donors by Cd vacancy acceptors, and demonstrate removal of the compensation by annealing to fill the vacancies. In a separate group of wafers, we find that an observed increase in absorption occurring during growth of a HgCdTe layer by liquid phase epitaxy can be explained in terms of an increase in Cd vacancies caused by diffusion of Cd to Te precipitates. This effect can be reversed by annealing in Cd-Zn vapor, which fills vacancies and eliminates some precipitates. Impurity concentrations were measured by glow discharge mass spectrometry (GDMS).
Document Type: Research Article
Publication date: June 1, 2001