Optical conductivity of Mn-doped GaAs

Abstract

The optical conductivity of the III–V diluted magnetic semiconductor compound (Ga, Mn)As was investigated theoretically. A direct comparison between the calculations and available experimental data is provided. We demonstrate that our model study is able to reproduce both qualitatively and quantitatively the measurements carried out by Burch et al (2006 Phys. Rev. Lett. 97 087208) and Singley et al (2002 Phys. Rev. Lett.89 097203, 2003 Phys. Rev. B 68 165204). It is found that an increase of the carrier density by up to one hole per Mn leads to a redshift of the broad conductivity peak located at approximately 200 meV in optimally annealed samples. Our study demonstrates that the non-perturbative treatment (beyond the valence band picture) is crucial for capturing these features. Otherwise a blueshift and an incorrect amplitude would result. We have calculated the Drude weight (order parameter) and have established the metal–insulator phase diagram. It is shown that (i) Mn-doped GaAs is indeed close to the metal–insulator transition and (ii) in both 5 and 7% doped samples, only 20% of the carriers are delocalized. Beyond the mobility edge, we found that the optical mass is mopt≈2me. Interesting new features of overdoped samples were found. The overdoped regime could be experimentally realized by Zn codoping. Detailed discussions and a careful analysis are provided.