A first principles study of sub-monolayer Ge on Si(001)

TL;DR

This study uses first-principles calculations to analyze the energetics and geometries of sub-monolayer Ge on Si(001), explaining the observed (2xn) reconstruction patterns through elastic relaxation effects.

Contribution

It provides a detailed first-principles analysis of the reconstruction energetics and explains the spacing of missing-dimer trenches based on elastic relaxation effects.

Findings

Formation energy depends strongly on trench spacing n.

Elastic relaxation accounts for the observed trench spacings.

Theoretical results match experimental observations for n ~ 8.

Abstract

Experimental observations of heteroepitaxial growth of Ge on Si(001) show a (2xn) reconstruction for sub-monolayer coverages, with dimer rows crossed by missing-dimer trenches. We present first-principles density-functional calculations designed to elucidate the energetics and relaxed geometries associated with this reconstruction. We also address the problem of how the formation energies of reconstructions having different stoichiometries should be compared. The calculations reveal a strong dependence of the formation energy of the missing-dimer trenches on spacing n, and demonstrate that this dependence stems almost entirely from elastic relaxation. The results provide a natural explanation for the experimentally observed spacings in the region of n \~ 8.