Electronic and structural properties of vacancies on and below the GaP(110) surface

TL;DR

This study uses first-principles calculations to analyze the atomic and electronic structures of vacancies on and below the GaP(110) surface, revealing relaxation behaviors, electronic states, and STM signatures.

Contribution

It provides detailed atomic and electronic structure data for surface and subsurface vacancies on GaP(110), including new insights into subsurface vacancy properties and their STM signatures.

Findings

Surface vacancies cause inward relaxation of neighboring atoms.

Vacancies exhibit mid-gap singly occupied electronic levels.

Subsurface vacancies show large relaxations and potential instability.

Abstract

We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and electronic structure of neutral surface and subsurface vacancies at the GaP(110) surface. The cation as well as the anion surface vacancy show a pronounced inward relaxation of the three nearest neighbor atoms towards the vacancy while the surface point-group symmetry is maintained. For both types of vacancies we find a singly occupied level at mid gap. Subsurface vacancies below the second layer display essentially the same properties as bulk defects. Our results for vacancies in the second layer show features not observed for either surface or bulk vacancies: Large relaxations occur and both defects are unstable against the formation of antisite vacancy complexes. Simulating scanning tunneling microscope pictures of the different vacancies we find excellent agreement with experimental data for the surface vacancies and predict the signatures of subsurface vacancies.