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

Abstract

A high minority carrier effective lifetime τeff 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 H2O vapor heat treatment. τeff 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 1.0×106 Pa H2O 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. τeff increased from 8.5×10-4 to 1.15×10-3 s probably caused by field effect passivation induced by hole trapping at the SiOx formed by H2O vapor heat treatment for 1 h. On the other hand, τeff was further increased to 1.2×10-3 s by 1.0×106 Pa H2O 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 τeff was observed by light illumination at the a-Si:H surface, probably because the SiOx clusters became stable and had no hole trapping property.