The photodiode converts incident light into a microcurrent that flows when photons of sufficient energy strike the device under reverse bias. In doing so, a leakage current is caused by the reverse bias. In order to decrease the leakage current, buffer layers are introduced as electron- and hole-blocking materials between the photoactive material and electrode. We fabricated an organic photodiode using Ga-doped NiOx as an electron-blocking layer and investigated the physical effects of Ga doping on the performance of the organic photodiode. Our results showed that this diode exhibited high detectivity of 1.06 x 10(12) Jones.