A brief review of our recent research on injection photodiodes based on metal oxide semiconductors deposited onto Si substrates is presented. A series of ZnSnO, NiO, and Zn1-xMgxO thin films are prepared by aerosol spray pyrolysis deposition or sol–gel spin coating on Si substrates with a post-deposition thermal treatment in air at a temperature of 500oC. The morphology of films is studied by scanning electron microscopy and atomic force microscopy, while their elemental composition and crystal structure are determined from energy dispersive X-ray (EDAX) and X-ray diffraction (XRD) analysis, respectively. It is shown that the produced n-ZnSnO/p-Si, n-ZnMgO/p-Si, and p-NiO/n-Si heterojunctions operate as injection photodiodes at a forward bias.