Electronic- and band-structure evolution in low-doped (Ga,Mn)As

TL;DR

This study investigates how low-level Mn doping affects the electronic and band structure of (Ga,Mn)As layers, revealing impurity band merging with the valence band and Fermi level shifts that influence magnetic properties.

Contribution

It provides experimental evidence for the evolution of band structure and impurity band merging in low-doped (Ga,Mn)As, clarifying the origin of ferromagnetism.

Findings

Band-gap transition energy decreases with low Mn doping in n-type (Ga,Mn)As.

Band-gap transition energy increases with higher Mn doping in p-type (Ga,Mn)As.

Results support the valence-band model for ferromagnetism in (Ga,Mn)As.

Abstract

Modulation photoreflectance spectroscopy and Raman spectroscopy have been applied to study the electronic- and band-structure evolution in (Ga,Mn)As epitaxial layers with increasing Mn doping in the range of low Mn content, up to 1.2%. Structural and magnetic properties of the layers were characterized with high-resolution X-ray diffractometry and SQUID magnetometery, respectively. The revealed results of decrease in the band-gap transition energy with increasing Mn content in very low-doped (Ga,Mn)As layers with n-type conductivity are interpreted as a result of merging the Mn-related impurity band with the host GaAs valence band. On the other hand, an increase in the band-gap-transition energy with increasing Mn content in (Ga,Mn)As layers with higher Mn content and p-type conductivity indicates the Moss-Burstein shift of the absorption edge due to the Fermi level location within the valence band, determined by the free-hole concentration. The experimental results are consistent with the valence-band origin of mobile holes mediated ferromagnetic ordering in the (Ga,Mn)As diluted ferromagnetic semiconductor.