Ferromagnetism and metallic state in digital (Ga,Mn)As heterostructures

TL;DR

This study uses density functional theory to analyze the electronic, magnetic, and transport properties of GaAs/AlAs digital ferromagnetic heterostructures with Mn doping, revealing effects of defects and band offsets on their half-metallicity and ferromagnetism.

Contribution

It provides a comprehensive theoretical analysis of how Mn doping, defects, and band offsets influence the electronic and magnetic properties of GaAs/AlAs heterostructures, highlighting conditions for robust ferromagnetism.

Findings

Defect-free heterostructures are half-metallic.

As antisites destroy half-metallicity, leading to metallic behavior.

Band offsets enhance ferromagnetic coupling and robustness.

Abstract

We present an extensive density functional theory study of the electronic, magnetic and transport properties of GaAs and AlAs digital ferromagnetic heterostructures. These can be obtained by $\delta$-doping with Mn the GaAs layers of a GaAs/AlAs superlattice. Our analysis spans a range of Mn concentrations and considers the presence of compensating defects such as As antisites. In the defect-free case all the heterostructures studied present an half-metallic electronic structure. In contrast when As antisites are present the half-metallic state is destroyed and the heterostructures behave as dirty planar metals. In this case they show a large $p$-type metallic conductance in the Mn plane mainly due to majority spin electrons, and an $n$-type hopping-like conductance in the GaAs planes mainly due to minority spin electrons. This suggests that if the As antisites can be kept far from the Mn planes, spatial separation of the different spin currents can be achieved. Finally we show that in the case of AlAs/(Ga,Mn)As digital ferromagnetic heterostructures the AlAs/GaAs valence band offset produces an additional confining potential for the holes responsible for the ferromagnetism. Therefore the ferromagnetic coupling between the Mn ions becomes larger and more robust to the presence of As antisites.