- Photoconductivity spectral response, linearity, and response time measurement indicate that surface effects and intergrain boundaries can play important roles in the characteristics of thin‐film Zn 3 P 2 . Response time of the order of a few seconds and the dependence of the spectral response on vacuum operation indicate the existence of long‐lived states at the surface. Photoconductivity response was found to be a maximum at a wavelength of 400 nm. Vacuum operation and heat treatment were observed to improve responsivity, shift the peak responsivity wavelength towards longer wavelengths, and increase the spectral width of maximum responsivity. The photoconductivity spectral dependence and the response times were found to be light–intensity dependent. It is proposed that effects of the barrier heights at the surface and at the intergrain junctions are light‐illumination dependent. The properties of the surface and the grain boundary depend on chemisorption or chemical reactions due to adsorbed gases or impurities.