Surface Defect Passivation and Reaction of c-Si in H2S.

A unique passivation process of Si surface dangling bonds through reaction with hydrogen sulfide (H2S) is demonstrated in this paper. A high-level passivation quality with an effective minority carrier lifetime (τeff) of >2000 µs corresponding to a surface recombination velocity of <3 cm/s is achieved at a temperature range of 550-650 °C. X-ray photoelectron spectroscopy (XPS) confirmed the bonding states of Si and S and provides insights into the reaction pathway of Si with H2S and other impurity elements both during and after the reaction. Quantitative analysis of XPS spectra showed that the τeff increases with an increase in the surface S content up to ∼3.5% and stabilizes thereafter, indicative of surface passivation by monolayer coverage of S on the Si surface. However, S passivation of the Si surface is highly unstable because of thermodynamically favorable reaction with atmospheric H2O and O2. This instability can be eliminated by capping the S-passivated Si surface with a protective thin film such as low-temperature-deposited amorphous silicon nitride.