Intrinsic and Extrinsic Contributions to the Lattice Parameter of GaMnAs

TL;DR

This study measures the lattice parameters and hole densities in GaMnAs to compare experimental results with DFT predictions, revealing discrepancies in the intrinsic lattice expansion caused by Mn incorporation.

Contribution

It provides the first direct experimental comparison of lattice parameters with DFT predictions, highlighting intrinsic lattice expansion in GaMnAs contrary to theoretical expectations.

Findings

Annealing reduces lattice constant less than predicted by DFT.

Measured lattice parameters remain larger than GaAs even at low compensation.

Intrinsic lattice parameter of GaMnAs is larger than GaAs, contradicting DFT predictions.

Abstract

We report on measurements of the crystal structure and hole density in a series of as-grown and annealed GaMnAs samples. The measured hole densities are used to obtain the fraction of incorporated Mn atoms occupying interstitial and substitutional sites. This allows us to make a direct comparison of the measured lattice parameters with recent density functional theory (DFT) predictions. We find that the decrease in lattice constant observed on annealing is smaller than that predicted due to the out diffusion of interstitial Mn during annealing. The measured lattice parameters after annealing are still significantly larger than that of GaAs even in samples with very low compensation. This indicates that the intrinsic lattice parameter of GaMnAs is significantly larger than that of GaAs, in contradiction to the DFT prediction.