Effects of substrate materials and their properties on photoassisted MOVPE of ZnSe using DMZn and DMSe as reactants have been investigated. For GaAs substrates, the presence of a thin predeposited ZnSe buffer layer and its quality greatly affect the subsequent film growth. However, for InP substrates, no essential effect of the buffer layer has been observed. Furthermore, in both substrates, the conduction type makes no significant difference to the results of photoassisted MOVPE. These results can be interpreted by a proposed growth model in which photoinduced excess holes In the ZnSe layer contribute to the film growth.