In this work, we investigate the spectral response of metal-oxide-semiconductor photodetectors based on Ge nanoclusters (NCs) embedded in a silicon dioxide (SiO2) matrix. The role of Ge NC size and density on the spectral response was evaluated by comparing the performance of PDs based on either densely packed arrays of 2 nm-diameter NCs or a more sparse array of 8 nm-diameter Ge NCs. Our Ge NC photodetectors exhibit a high spectral responsivity in the 500–1000 nm range with internal quantum efficiency of ~ 700% at − 10 V, and with NC array parameters such as NC density and size playing a crucial role in the photoconductive gain and response time. We find that the configuration with a more dispersed array of NCs ensures a faster photoresponse, due to the larger fraction of electrically-active NCs and the partial suppression of recombination centers. The photoconduction mechanism, assisted by …