A detailed investigation of the compositional, optical and electrical properties of a chromium silicide layer grown at room temperature on top of doped amorphous silicon films is presented. The formation of the layer is promoted only when phosphorous atoms are present in the film. The deposition of a very thin n-type doped layer (around 5nm) on top of a p-type doped film has allowed us to achieve the chromium silicide formation also on p-type material without changing its doping properties. Angle resolved X-ray photoelectron spectroscopy measurements demonstrate the presence of chromium-oxide, chromium silicide and metallic chromium in similar percentages for both p- and n-type doped layers. From the ellipsometric analysis, the refractive index spectra have been extracted, and the layer thickness has been estimated to be 5nm for both p- and n-type doped layers. From planar conductivity measurements, we have found that the chromium silicide promotes an activation energy reduction from 0.24eV down to 0.017eV for the n-type layer and from 0.36eV down to 0.14eV for the p-type film.