First-principles study of the H2S passivation on 6H-SiC (0001) surface

Passivation is an effective way to reduce density of states (DOS) on the surface. In order to verify the differences and stabilities of H₂S passivation on Si- and C-face of 6H-SiC, the adsorption of H₂S on surface is studied by the first principles method, which is based on the density functional theory. Adsorption configuration and stability are researched with the coverage changing from 1/9monolayer (ML) to 1/3ML on Si-face while 1/9ML to 5/9ML on C-face. Adsorption energy, DOS and charge population of the system are calculated separately. On Si-face, energy calculations show that H₂S which is adsorbed at the bridge (BR) site is more stable than that adsorbed at the on-top (OT) site. After H₂S is decomposed, S atoms are combined at the BR site, while H atoms are adsorbed at the OT site. The surface states are noticeably reduced after passivation. Surface states are reduced to the lowest when the coverage is 2/9ML. On C-face, H₂S which is adsorbed at the OT site is more stable than that adsorbed at the BR site. After H₂S is decomposed, HS bonds and H atoms are all combined at the OT site. The surface states are noticeably reduced to the lowest when the coverage is 4/9ML.