Universal valence-band picture of the ferromagnetic semiconductor GaMnAs

TL;DR

This study reveals that the valence band structure of GaMnAs remains largely similar to GaAs, with the Fermi level in the bandgap and minimal p-d exchange splitting, clarifying the origin of ferromagnetism in this material.

Contribution

The paper provides a universal valence-band picture of GaMnAs, showing the band structure is unaffected by Mn doping and the Fermi level resides in the bandgap.

Findings

Fermi level is in the bandgap across samples

Valence band structure remains similar to GaAs

p-d exchange splitting is only a few meV

Abstract

The origin of ferromagnetism in the prototype ferromagnetic semiconductor GaMnAs is still controversial due to the insufficient understanding of its band structure and Fermi level position. Here, we show the universal valence-band (VB) picture of GaMnAs obtained by resonant tunneling spectroscopy for a variety of surface GaMnAs layers with the Mn concentrations from 6 to 15% and the Curie temperatures from 71 to 154 K. We find that the Fermi level exists in the bandgap, and that the VB structure of GaAs is almost perfectly maintained in all the GaMnAs samples, i.e. VB is not merged with the impurity band. Furthermore, the p-d exchange splitting of VB is found to be quite small (only several meV) even in GaMnAs with a high Curie temperature (154 K). These results indicate that the VB structure of GaMnAs is quite insensitive to the Mn doping.