Origin of the anomalous magnetic circular dichroism spectral shape in ferromagnetic (Ga,Mn)As: Impurity bands inside the band gap

TL;DR

This study uses magnetic circular dichroism spectroscopy to reveal that impurity bands within the band gap significantly influence the optical and magnetic properties of ferromagnetic (Ga,Mn)As, challenging previous assumptions about hole doping.

Contribution

It demonstrates that impurity bands cause the positive MCD background and clarifies the nature of p-d exchange interactions in (Ga,Mn)As.

Findings

Impurity bands cause strong positive MCD background.

E0 transition MCD signal is negative, indicating antiferromagnetic p-d exchange.

Hole doping of the valence band is less than previously thought.

Abstract

The electronic structure of a prototype dilute magnetic semiconductor (DMS), Ga1-xMnxAs, is studied by magnetic circular dichroism (MCD) spectroscopy. We prove that the optical transitions originated from impurity bands cause the strong positive MCD background. The MCD signal due to the E0 transition from the valence band to the conduction band is negative indicating that the p-d exchange interactions between the p-carriers and d-spin is antiferromagnetic. The negative E0 MCD signal also indicates that the hole-doping of the valence band is not so large as previously assumed. The impurity bands seem to play important roles for the ferromagnetism of Ga1-xMnxAs.