Mechanisms of monovacancy annihilation and type-A defect creation on Si(0 0 1)–2 × 1

Based on first principles quantum mechanics (DFT/GGA with pseudopotentials) calculations, we propose a new mechanism for monovacancy annihilation and single missing dimer creation. Our study shows that an isolated monovacancy can exist fairly stable, rather than liberating the remaining atom of the `defectʹ dimer readily. The liberation barrier is calculated to be 1.3 eV. However, the monovacancy can diffuse rapidly along a dimer row by overcoming a barrier of 0.3 eV, leading to vacancy–vacancy pairing at elevated temperatures. These results suggest that the vacancy–vacancy pairing may play a major role in creating a single missing-dimer vacancy (which is ≈1.8 eV more stable than two isolated monovacancies). We also present the pathways and barriers of (i) the remaining atom hopping between the buckled-up and down site of the `defectʹ dimer and (ii) the vacancy diffusion into the subsurface layer.