Photocapacitance measurement is applied to investigate the stoichiometry-dependent deep levels inp-type InP crystals doped with Zn prepared by 4 h annealing at 700 °C under controlled phosphorus vapor pressure. Photocapacitance results reveal three dominant deep levels. A dominant deep level at 1.05 eV above the valence band is detected commonly before and after annealing, and the change of level densities is shown as a function of the phosphorus vapor pressure. Another two deep levels are also detected after annealing at 0.74 eV above the valence band and at 0.51 eV below the conduction band. In view of the deviation from the stoichiometric composition of InP, possible origins of these levels and their optical transition mechanism are discussed. ©1997 American Institute of Physics.