The low temperature deposition of a-Si:H films and devices by mercurysensitized photo-decomposition of silanes is described. The problem of window deposition is ameliorated by the use of a perfluoropolyether coating to give deposition rates of 0.3 Å s−1. Highly photosensitive undoped layers can be produced. These films exhibit many properties in common with glow discharge films including thermal quenching of photoconductivity between 125-200°K and the Staebler-Wronski effect. A wide gap silicon carbide p layer is described, and is usefully employed in p-i-n structures to give 6% efficient solar cells. SIMS analysis of these devices shows that it is possible to achieve sharp p-i interfaces in a single chamber reactor. Deposition rates greater than 2 As−1 have recently been achieved.