Time-Dependence of Zinc Diffusion in Gallium Arsenide under a Concentration Gradient

Abstract

The diffusion profiles of under a concentration gradient have been determined as a function of diffusion time for diffusions at 600° and 750°C. Pure radioactive Zn65 is used as the diffusion source. It is found that local equilibrium is not reached for these diffusions since the diffusion profiles can not be expressed in terms of a single variable . When the diffusion depth is plotted against the square root of diffusion time, a linear relationship is not obtained. The deviation from linear relationship is found to be quite pronounced at lower diffusion temperatures, and less so at higher diffusion temperatures. These observations indicated that the diffusion process can not be described by Fick's second law (with a concentration‐dependent effective diffusion coefficient, . Under this condition, the Boltzmann‐Matano analysis which has been used quite extensively to obtain values of the effective diffusion coefficient of from the diffusion profiles of is not valid. Results are discussed in terms of nonequilibrium in the interstitial‐substitutional diffusion. Complications due to the presence of diffusion‐induced defects are also described.