Diffusion and Solubility of Zinc in Gallium Phosphide Single Crystals

Abstract

Radiotracer Zn⁶⁵ has been diffused into 0.2‐Ω cm sulfur‐doped GaP single crystals from constant pressure vapor sources. Solid solubilities have been measured at temperatures between 800° and 1100°C, the diffusion profiles have been obtained and these have been analyzed by the Matano method. Although retrograde solid solubility is expected at higher temperatures, the data below 1100°C are an excellent fit to the relation C=2.6×10²³ exp(−0.85/kT). The diffusion coefficient is found to be concentration‐dependent. At temperatures below 900°C the diffusion coefficient can be represented by the empirical expression D=7.5×10⁻⁸ C^0.45 exp(−2.50/kT). Above 900°C the profiles are similar to those of Zn in GaAs and the diffusion coefficient varies approximately as the square of the zinc concentration. The results are interpreted and the diffusion mechanism is discussed in terms of parallel‐mode diffusion of interstitial and substitutional zinc.