Plasma-enhanced atomic layer deposition is an attractive method for producing n-GaP layers at low temperatures on p-Si wafers for further photovoltaic application of n-GaP/p-Si heterostructures. In this study, we explore the influence of growth conditions on the electrophysical quality of thin n-GaP layers. It was established from admittance spectroscopy and current-voltage characteristics that the activation energy of conductivity in GaP decreases from 0.08 eV to 0.04 eV, with an increase in phosphine flow during the phosphorous step, and a subsequent drop to an extremely low value (< 0.02 eV) when additional flow of silane was added. This leads to extreme improve photovoltaic performance of the ITO/n-GaP/p-Si sample due to suppression of inflection on the I–V curve leading to an increase in the short-circuit current and the fill factor. Fruthermore, a deep level with the activation energies ranging from 0.50 to 0.55 eV and the capture cross-section σT = (1–10)·10–16 cm2 was detected in all layers.