Zinc is diffused into undoped InP epitaxial layers in a metalorganic chemical vapor deposition reactor using DMZn as a source. Using an interstitial-substitutional model, the effective diffusivity of zinc in undoped InP is expressed uniquely as a function of the sum of the zinc-phosophorous vacancy complex and substitutional zinc concentrations assuming a negligible interstitial zinc concentration. Boltzmann-Matano analysis of secondary ion mass spectroscopy profiles for the total zinc concentration supports a neutral (m = 0) charge on the interstitial zinc. (C) 2004 American Vacuum Society.