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 (τ_eff) 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 τ_eff 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.