Effect of annealing on the depth profile of hole concentration in (Ga,Mn)As

TL;DR

This study investigates how annealing at 250°C affects the hole concentration depth profile, Mn distribution, and magnetic properties of thick (Ga,Mn)As layers, revealing the importance of initial gradients and challenging the out-diffusion model.

Contribution

It demonstrates that annealing modifies the existing hole concentration gradient in (Ga,Mn)As layers and suggests alternative mechanisms beyond Mn out-diffusion for changes in conductivity.

Findings

Annealing influences the vertical hole concentration gradient.

The change in carrier profile is not mainly due to Mn out-diffusion.

Initial gradients are crucial for understanding conductivity and magnetization.

Abstract

The effect of annealing at 250 C on the carrier depth profile, Mn distribution, electrical conductivity, and Curie temperature of (Ga,Mn)As layers with thicknesses > 200 nm, grown by molecular-beam epitaxy at low temperatures, is studied by a variety of analytical methods. The vertical gradient in hole concentration, revealed by electrochemical capacitance-voltage profiling, is shown to play a key role in the understanding of conductivity and magnetization data. The gradient, basically already present in as-grown samples, is strongly influenced by post-growth annealing. From secondary ion mass spectroscopy it can be concluded that, at least in thick layers, the change in carrier depth profile and thus in conductivity is not primarily due to out-diffusion of Mn interstitials during annealing. Two alternative possible models are discussed.