Surface Passivation of Crystalline Silicon by Combination of Amorphous Silicon Deposition with High-Pressure H2O Vapor Heat Treatment

A high minority carrier effective lifetime $\tau_{\text{eff}}$ of crystalline silicon was achieved by hydrogenated amorphous silicon (a-Si:H) films formed by a combination of plasma-enhanced chemical vapor deposition at 150 °C with high-pressure H 2 O vapor heat treatment. $\tau_{\text{eff}}$ was $1.6\times 10^{-4}$, $3.0\times 10^{-4}$, and $1.15\times 10^{-3}$ s for n-type silicon substrates coated with 3-, 10-, and 50-nm-thick a-Si:H films treated with $1.0\times 10^{6}$ Pa H 2 O vapor heat treatment between 180 and 300 °C for 1 h. Light-induced passivation enhancement was demonstrated when 620-nm light was illuminated at the 50-nm-thick a-Si:H surface. $\tau_{\text{eff}}$ increased from $8.5\times 10^{-4}$ to $1.15\times 10^{-3}$ s probably caused by field effect passivation induced by hole trapping at the SiO x formed by H 2 O vapor heat treatment for 1 h. On the other hand, $\tau_{\text{eff}}$ was further increased to $1.2\times 10^{-3}$ s by $1.0\times 10^{6}$ Pa H 2 O vapor heat treatment at 300 °C for 3 h for the sample formed with the 50-nm-thick a-Si:H film. However, no increase in $\tau_{\text{eff}}$ was observed by light illumination at the a-Si:H surface, probably because the SiO x clusters became stable and had no hole trapping property.