Effects of the substrate temperature on the growth and properties of hydrogenated nanostructured silicon thin films

Nanostructured silicon thin films were deposited by a pulsed plasma enhanced chemical vapour deposition process using an argon-silane mixture. For each deposition temperature (T_s), the plasma modulation was chosen in such a way that the discharge was switched off just before the onset of powder formation. The optical and electrical properties of the films were investigated as a function of T_s and compared to those of films deposited under the same plasma conditions but with a continuous wave (CW) plasma. While the CW films show a gradual improvement in their properties with increasing T_s, a drastic change appears in the optical and electrical properties of hydrogenated nanostructured silicon (ns-Si:H) films for T_s > 50 °C. In particular, for a deposition temperature of 150 °C a more compact material with a small surface roughness and a high conductivity was obtained. This improvement is correlated to the discharge conditions and particularly to the small size of the clusters embedded in the deposited film.