We report the electrical and optical properties of P-doped epitaxial ZnO thin films grown heteroepitaxially on sapphire substrates or homoepitaxially on ZnO wafers grown by the hydrothermal method, respectively. As-grown heteroepitaxial thin films exhibit semi-insulating to strongly n-conducting behavior depending on the P-content and the oxygen partial pressure applied during deposition. New features are observed in the recombination spectra compared to nominally undoped ZnO thin films. The spectral position of these new features also depends on the growth conditions making a clear correlation between P-incorporation and particular spectral features feasible. For the homoepitaxially grown thin films lateral scanning capacitance microscopy measurements revealed areas of both n- and p-type majority carriers.