Nanocrystalline silicon films directly made by pulsed-DC magnetron sputtering

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared by a pulsed-DC magnetron sputtering method using an argon/hydrogen mixture gas. The effects of working pressure and hydrogen concentration on the structural and electrical properties of the films were systematically investigated using grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, and conductivity measurement. A threshold working pressure of around 14 mTorr and a minimum hydrogen concentration of about 70% were found necessary before any crystallinity was detectable. These findings were rationalized using the concept of surface diffusion model for crystalline growth. The deposition rate decreased monotonically with increasing hydrogen concentration, while the conductivity varied with crystallite size. The abnormally low conductivity level of these nc-Si:H films was due to the extraordinarily high defect density, which was in turn attributed to both the enhanced ion bombardment from the pulsed-DC plasma and the oxygen contamination from the target.