Thin silicon films deposited at low substrate temperatures studied by surface photovoltage technique

Investigation of hydrogenated microcrystalline silicon (μc-Si:H) thin films for solar cells deposited at very low substrate temperatures is motivated by further reduction of the energy budget and a possibility to use practical polymer substrates. We have applied the surface photovoltage (SPV) technique in an expanded spectral region (1.2–3 eV) to study transport properties of μc-Si:H thin films deposited at substrate temperatures between 35 and 200 °C. The application of the SPV technique revealed new phenomena of low-temperature μc-Si:H growth (e.g. formation of a bottom barrier for deposition temperatures below 100 °C, presence of a defective layer for deposition temperatures 75–200 °C) without performing any additional measurements. Good separation of top and bottom space charge regions was detected even for the sample thickness less than 0.5 μm. By increasing the deposition temperature, a transition from the amorphous to microcrystalline growth was crossed. However, it seems not to be sharp—the experimental data indicate at least three different growth regimes.