A thin intrinsic hydrogenated amorphous silicon (i-a-Si:H) layer was used to improve the performance of Si metal-semiconductor-metal photodetectors (MSM-PDs). At a bias of 10V, this a-Si:H MSM-PD had a rise time of 25ps and an FWHM of 55ps for temporal response, a dark current density of 690fA/mu m(2), a responsivity of 0.7 A/W and a spectral response peaking at 700nm.