Ge vacancies atGe∕Siinterfaces: Stress-enhanced pairing distortion

Abstract

We have performed first-principles total-energy electronic-structure calculations based on the densityfunctional theory to clarify energetics and electron states of the Ge vacancies in strained Ge layers on the Si͑001͒ surface. We find that pairing distortion is a principal relaxation pattern around the vacancies. The pairing of the two atoms located on either ͑110͒ or ͑110͒ plane is remarkably enhanced due to compressed strain in the lateral plane. It is found that the enhanced pairing causes reduction of formation energies, disappearance of deep levels in the monovacancy, deep-level crossing in the divacancy, and arrangement of the trivacancy on the ͑110͒ or the ͑110͒ plane. We have also found that the vacancy at the very interface layer facing the Si substrate is energetically unfavorable due to the larger energy cost to generate Si dangling bonds compared with Ge dangling bonds upon removal of atoms.

Generation of Acceptor Levels in Ge by the Uniaxial Strain - A Theoretical Approach

“…First, we show the results of biaxial strain. We investigated the strained Ge films on Si substrates (5). We have found that the formation energies of vacancies in the strained Ge are about 1.5 eV, and these formation energies are substantially smaller compared with that in bulk Ge (2.7 eV).…”

“…Now the enhancement of mobility is observed in strained materials, so heterostructures consisting of Si and Ge have been attracting much greater attention regarding one of promising boosters for post-scaling Si technology (4). However, there are a few reports related to atomic and electronic structures of Ge defects under strain in spite of their importance, although we have theoretically reported the Ge vacancies under biaxial strain (5). In this paper, we investigate the energetics and atomic and electronic structures of Ge mono-vacancies under compressive strain.…”