Studies on the diffusion of zinc and iodine into CdTe

Abstract

Studies on the diffusion of iodine and zinc into CdTe are reported. Each iodine profile was divided up into four distinct regions and described mathematically by a function consisting of the sum of four complementary error functions. When plotted on an Arrhenius graph, the diffusivities gave four straight line relationships with similar slopes and the Arrhenius parameters for the fastest component of D₀₁ = (7 ±3). 10^-11 cm² s^-1 and E₁ = (0.21 ±0.05) eV. When extrapolated down to 20°C this gave a diffusivity of 10^-14 cm² s^-1 indicating that when iodine is diffused from the vapor it is not suitable as a long term stable dopant in devices where sharp impurity profiles are required. In the case of the zinc diffusions, each profile can be divided into two parts and was fitted satisfactorily by the sum of two complementary error functions giving two values of the diffusivities: D_slow due to zinc diffusion into the slice from the vapor and D_fast due to interdiffusion between a surface layer of Zn_x Cd_1-x Te formed on the slice and the remaining CdTe.