First-principles total-energy electronic-structure calculations were performed, based upon density-functional theory, in order to clarify the energetics and electron states of the Ge vacancies in strained Ge layers on the Si(001) surface. It was found that pairing distortion was a principal relaxation pattern around the vacancies. The pairing of the 2 atoms located on either the (110) or (1¯10) plane was markedly enhanced due to compressed strain in the lateral plane. It was found that the enhanced pairing caused a reduction in formation energies, the disappearance of deep levels in the monovacancy, deep-level crossing in the divacancy and arrangement of the trivacancy on the (110) or the (1¯10) plane. It was also found that the vacancy at the interface layer facing the Si substrate was energetically unfavorable due to the larger energy cost required to generate Si dangling bonds, compared with Ge dangling bonds, upon the removal of atoms.

Ge Vacancies at Ge/Si Interfaces - Stress-Enhanced Pairing Distortion. K.Takai, K.Shiraishi, A.Oshiyama: Physical Review B, 2008, 77[4], 045308 (8pp)