Photoresponse of the Au/(Er2O3:PVC)/n-Si diode was executed in a wide range of illumination intensity (P). Its basic electrical parameters such as ideality factor (n), barrier height (ΦB0), series and shunt resistances (Rs, Rsh), photocurrent (Iph), energy-dependence of interface states (Nss), and photosensitivity (S) were calculated from the results of the current–voltage (I–V) measurements. At the negative-bias region, an increase in Iph is observed due to the e−-h+ pairs that occur as a result of increasing P and their drift in opposite directions under the internal electric field. The ln(Iph)–ln(P) plot shows a good linear behavior under various applied voltages. Their slopes vary from 1.47 to 1.64, indicating that empty trap levels, that is, levels not occupied by charges, are of low density. The values n, ΦB0, and Rs were obtained using the thermionic emission theory, Cheung, and Norde functions. The value of ΦB0 decreases with increasing n and P as linearly with ΦB0(n) = (−0.143n + 1.118) eV and ΦB0(P) = (−2 × 10−4P + 0.831) eV, respectively. This illumination coefficient of ΦB0 (=−2 × 10−4 eV/[mW/cm2]) is close to the temperature coefficient bandgap of Si (=−4.73 × 10−4 eV/K). These results show that the performed Au/(Er2O3:PVC)/n-Si diode has excellent photo-response and can be successfully used in photovoltaic applications instead of conventional metal–semiconductor diodes.