This paper is concerned with the choice and influence of the deposition conditions of ITO thin films ontop‐type single crystal InP substrates for use as heterojunction solar cells. Our analyses, based on capacitance–voltage, current–voltage, spectral response, surface photovoltage, and reflection electron diffraction, indicate that adverse effects of the deposition process on the surface can be reduced by proper choice of deposition schedule. The general conclusions are (1) The reverse saturation current is 2–3 orders of magnitude lower for cells fabricated by using very low power deposition of the ITO than for those using high power deposition. (2) Either abrupt or graded interfaces can be formed depending on the input power to the sputtering process. (3) The extent of the grading increases with increased rf power input and is believed to be due to the diffusion of species (possibly of tin).