We propose in this work, contact Schottky Nickel/porous silicon (PSi) system, coupled to nanocrystallites size variation of material for a possible technique to reduce dark current. The device consists of metal- semiconductor-metal photodiode (MSM-PD). Higher barrier ΦΒ enhances the performance of MSM-PD through reduction in dark current (Is), and benefits to resolve noise from signal detection of the devices. In order to reduce much more Is, we proposed different anodization times (5–7–10 min) as method to tune the size of nanocrystallites. As result Is value was reduced to almost two orders of magnitude for 10 min etching time, and the value of Is ≈ 10–10 A. ΦΒ reached the value of 0.882 eV. Among the hypothesis suggested in the reduction of Is was the quantum confinement effects. According to Rhoderick model, the Schottky barrier height is explicitly linked to the band gap energy due to the presence of interface states. The existence of narrow nanocrystallites increased energy band gap of PSi and the Schottky barrier height, which in turn reduces Is. The photoluminescence measurements confirmed our hypothesis. Photosensitivity of the device was established by adopting the MSM configuration, and strong absorption was detected in visible range.