Formation mechanism of multivacancies on H-passivated and Si-reconstructed surfaces of 6H–SiC (0001): a DFT calculation

Abstract

The clarification of formation mechanism of surface vacancies (mono-, di-, and multivacancy) is of great help to the defect and electronic engineering of functional crystalline solids. Herein we use the density functional theory (DFT) calculations to elucidate the formation mechanism and evolution paths of vacancies within the Si–C atomic bilayers on H-passivated (H-P) and () R 30° Si-reconstructed (S-R) 6H–SiC (0001) surfaces. The calculation results of formation energies (Efs) reveal that Si monovacancies (VSi) prefer to form within the first outer Si–C bilayer while two isolated VSi and C monovacancies (VC) are more likely to aggregate into a VSiVC divacancy on both selected surfaces. In particular, Efs of multivacancies (Vns) with different missing Si/C atoms (n = 3 ∼ 10) and spatial configurations were systematically calculated and compared, from which the lowest energy paths (LEPs) of Vns for two kinds of surfaces are clarified. For n ≤ 6, Vns tend to expand within the two-dimensional (2D) first Si–C bilayer but they will expend vertically into the underneath Si–C bilayers when n > 6. The fitted curves of resultant LEPs disclose that the 2D evolution of the multivacancy is the main evolution form with high symmetric Vns being dominant on the 6H–SiC (0001) surfaces.