Undoped silicon thin films were deposited by a radio frequency plasma enhanced chemical vapor deposition technique over a wide range of substrate temperatures (170-370℃) using a mixture of silane and hydrogen gas. A low power density (35 mW cm~(-2)) was chosen. The effects of substrate temperature on the structural properties of the films was studied. A distinct transition from amorphous to microcrystalline phase is observed with an increase in the substrate temperature (T_(s)). Raman spectroscopy shows the variation of amorphous and crystalline volume fractions in the silicon films. The amorphous matrix seems to be composed mainly of monohydrides in contrast to the usual dominance of polyhydrides. At the onset of crystallinity, the films have tiny crystallites and the grain size (δ) increases with T_(s) (at T_(s)～370℃, δ～350 A). The deposition rate increases with T_(s) and attains its maximum (28.2 A min~(-1)) at the amorphous to microcrystalline transition region. All the microcrystalline films with their differing crystallinities degrade less than their amorphous counterparts under light exposure. The film prepared at the edge of crystallinity shows considerable photosensitivity (photogain of ～10~(3)).
展开▼
