Surface Passivation of Crystalline Silicon by Combination of Amorphous Silicon Deposition with High-Pressure H_2O Vapor Heat Treatment

摘要

A high minority carrier effective lifetime r_et 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℃ with high-pressure H_2O vapor heat treatment. Reff was 1.6 × 10~(-4), 3.0 × 10~(-4), and 1.15 × 10~(-3) s for n-type silicon substrates coated with 3-, 10-, and 50-nm-thick a-Si:H films treated with 1.0 × 10~6 Pa H_2O vapor heat treatment between 180 and 300 ℃ for 1 h. Light-induced passivation enhancement was demonstrated when 620-nm light was illuminated at the 50-nm-thick a-Si:H surface. τ_(eff) increased from 8.5 × 10~(-4) to 1.15 × 10~(-3)s probably caused by field effect passivation induced by hole trapping at the SiO_x formed by H_2O vapor heat treatment for 1 h. On the other hand, τ_(eff) was further increased to 1.2 × 10~(-3)s by 1.0 × 10~6 Pa H_2O vapor heat treatment at 300℃ for 3h for the sample formed with the 50-nm-thick a-Si:H film. However, no increase in T_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.