Diffusion and clustering of substitutional Mn in (Ga,Mn)As

TL;DR

This study investigates how gallium vacancies influence the diffusion and clustering of manganese in (Ga,Mn)As during growth and annealing, revealing mechanisms that affect magnetic properties.

Contribution

It provides a multi-scale analysis combining first-principles calculations and kinetic Monte Carlo simulations to elucidate vacancy-mediated Mn diffusion and clustering.

Findings

Gallium vacancies enable Mn diffusion during annealing.

Clustering of Mn reduces the Curie temperature.

Fast interstitial Mn diffusion explains annealing behavior.

Abstract

The Ga vacancy mediated microstructure evolution of (Ga,Mn)As during growth and post-growth annealing is studied using a multi-scale approach. The migration barriers for the Ga vacancies and substitutional Mn together with their interactions are calculated from first principles, and temporal evolution at temperatures ranging from 200 to 350$^\circ$C is studied using Lattice Kinetic Monte Carlo simulations. We show that at the typical growth and annealing temperatures (i) gallium vacancies provide the diffusion mechanism for substitutional Mn and (ii) in 10--20 h the vacancy mediated diffusion of Mn promotes the formation of substitutional clusters. Clustering reduces the Curie temperature ($T_C$), and therefore the Mn clustering combined with the fast interstitial Mn diffusion explains the experimentally observed twofold annealing behavior of $T_C$.