Diffusion of gallium in cadmium telluride

Abstract

The diffusion of Ga into bulk-grown, single crystal slices of CdTe was studied in the temperature range 350–811°C where the diffusion anneals were carried out in sealed silica capsules using three different types of diffusion sources. These were: excess Ga used alone, or with either excess Cd or excess Te added to the Ga. Each of the three sets of conditions resulted in different types of concentration profile. At temperatures above 470°C, a function composed of the sum of two complementary error functions gave the best fit to the profiles, whereas below this temperature a function composed of the sum of one or more exponentials of the form exp (− ax) gave the best fit. The behaviour of the diffusion of Ga in CdTe is complex, but it can be seen that two diffusion mechanisms are operating. The first is where D appears to decrease with Cd partial pressure, which implies that the diffusion mechanism may involve Cd vacancies, and a second which is independent of Cd partial pressure. The moderate values of D obtained, confirms that CdTe buffer layers may be useful in reducing Ga contamination in ( Hg x Cd 1−x )Te epitaxial devices grown on GaAs substrates.