Model for nucleation in GaAs homoepitaxy derived from first principles

TL;DR

This study uses first-principles calculations to model nucleation during GaAs homoepitaxy, revealing that stable nuclei are Ga adatom pairs and that nucleation favors regions with partial trench filling.

Contribution

It provides a detailed atomic-scale model of nucleation mechanisms in GaAs MBE growth based on density functional theory calculations.

Findings

Ga adatom pairs form stable nuclei via dimerization or substrate interaction

As_2 adsorption is highly exothermic on Ga dangling bond sites

Nucleation prefers regions with partial trench filling on the surface

Abstract

The initial steps of MBE growth of GaAs on beta 2-reconstructed GaAs(001) are investigated by performing total energy and electronic structure calculations using density functional theory and a repeated slab model of the surface. We study the interaction and clustering of adsorbed Ga atoms and the adsorption of As_2 molecules onto Ga atom clusters adsorbed on the surface. The stable nuclei consist of bound pairs of Ga adatoms, which originate either from dimerization or from an indirect interaction mediated through the substrate reconstruction. As_2 adsorption is found to be strongly exothermic on sites with a square array of four Ga dangling bonds. Comparing two scenarios where the first As_2 gets incorporated in the incomplete surface layer, or alternatively in a new added layer, we find the first scenario to be preferable. In summary, the calculations suggest that nucleation of a new atomic layer is most likely on top of those surface regions where a partial filling of trenches in the surface has occurred before.