Characterization of Microcrystalline Transition from Amorphous Silicon as a Function of Hydrogen Dilution and Substrate Temperature of Hot-Wire CVD

a-Si:H films were prepared by hot wire chemical vapor deposition. One group was deposited at a substrate temperature of T_s=250°C with varied hydrogen-dilution ratio, O<R<10; the other group was deposited with fixed R=3 but a varied T_s from 150 to 550°C. IR, Raman and PL spectra were studied. The Raman results indicate that there is a threshold value for the microstructure transition from a- to μc-Si. The threshold is found to be R ≈ 2 at T_s = 250°C and T_s ≈ 200°C at R=3. The IR absorption of Si-H at 640 cm^-1 was used to calculate the hydrogen content, C_H. C_H decreased monotonically when either R or T_s increased. The Si-H stretching mode contains two peaks at 2000 and 2090 cm^-1. The ratio of the integral absorption peaks I₂₀₉₀/(I₂₀₉₀+I₂₀₉₀) showed a sudden increase at the threshold of microcrystallinity. At the same threshold, the PL features also indicate a sudden change from a- to μc-Si., i.e. the low energy PL band becomes dominant and the PL total intensity decreases. We attribute the above IR and PL changes to the contribution of microcrystallinity, especially the c-Si gain-boundaries.