In studying the growth of epitaxial layers in III-V compounds, it is advantageous to obtain information on the early stage of the growth that takes place at the substrate-epitaxial layer interface. In this paper, we describe a method of measuring the recombination velocity at this interface, as well as the minority carrier diffusion length in the bulk of the epitaxial layer. A bi-directional diffusion of excess carriers was modeled, with layer thickness, diffusion length and recombination velocity as variables. Layer thickness was determined using spreading resistance, the other two variables can be separated by measuring layers of several thicknesses. Some carriers diffuse from the point of generation toward the surface and are collected at a Schottky barrier depletion layer, The remaining carriers diffuse from the point of generation toward the epi-substrate interface where they recombine.