The zinc diffusion process into InP through a thin InGaAs layer using diethylzinc (DEZn) as a p-dopant source was investigated. The distribution profiles of electrically active dopant in InGaAs/InP heterostructures were obtained by electrochemical capacitance-voltage profiling technique. The influence of temperature and pressure in the reactor, DEZn flow rate and process time on the concentration of holes and the diffusion depth was investigated. The process of zinc diffusion strongly depends on the zinc concentration at the surface, however, the maximum concentration of holes and the depth of zinc diffusion into the InP layer might be chosen independently in a certain range of values.