The Cu/Sn-LaPO4/n-Si MIS Schottky barrier diode (SBD) with a 10% Sn doping has been successfully fabricated, and their photodiode properties were investigated. The I-V forward and reverse bias curves determine the photodiode parameters such as barrier height, ideality factor, and saturation currents from the thermionic emission theory. The results of the experiments with 10% Sn-LaPO4 SBDs showed a linear decrease in the ideality factor (n) up to 2.31 and 1.74, respectively, with a small increase in the effective barrier height (?B) of 0.744 and 0.806 eV in dark and light conditions these results signify their use in optoelectronic industries.