Sources for cadmium diffusion in InP kinetics in short duration anneals

Short duration cadmium diffusion in sealed ampoules was studied at a temperature of 550°C and a Cd/P molar ratio of 0.28. The starting sources were physical mixtures of either elemental Cd metal and red P or Cd₃P₂ and red P. The Cd profiles were determined by SIMS. In relatively short diffusion anneals up to two hours, the surface concentration, or solubility of Cd with either diffusion source is the same. However, Cd penetration was shallower in samples diffused with elemental (Cd,P) mixture than in samples diffused with (Cd₃ P₂,P) mixture as the starting source. The slower diffusion of Cd with elemental starting source (Cd,P) appears to be related to the kinetics involved in reaching the thermal equilibrium between CdP₂ and CdP₄. The formation of Cd₃ P₂ en route to the eventual formation of CdP₂ and CdP₄ or surface related kinetics are proposed as plausible mechanisms. The results appear to be consistent with the establishment of thermal equilibrium between CdP₂ and CdP₄ at a Cd/P ratio of 0.28 per the available phase equilibria data. The diffusion kinetics and defect structure are discussed on the basis of quasi-equilibrium among the three condensed phases InP, CdP₂ and CdP₄