Diffusion of Cadmium in Gallium Arsenide

Abstract

The diffusion process of cadmium into gallium arsenide from the gaseous phase has been investigated as a function of temperature and arsenic vapor pressure by means of the radio-activation analysis and electrical conductivity method. The diffusion profile of cadmium without excess arsenic vapor follows the complementary error functions and its temperature dependence can be described well by the equation D=D ₀exp (-E/kT), where E, the activation energy of diffusion, is 2.2 eV and D ₀ is 1.3×10^-3 cm² sec^-1. The surface concentrations and the diffusion depth of cadmium increase as the cadmium vapor pressure increases. Under the excess arsenic vapor, the diffusion profiles of cadmium are given by two overlapping complementary error functions. The effective diffusion coefficients of cadmium, as obtained from both branches of the diffusion profiles, are found to increase in proportion to the fourth root of the arsenic vapor pressure. These results suggest that the diffusion of cadmium into gallium arsenide proceeds through the gallium sublattice of the crystal.