Ellipsometric study of the electronic structure of Ga1−xMnxAs and low-temperature GaAs

We have measured the optical constants of Ga1−xMnxAs from 0.62 to 6 eV, using spectroscopic ellipsometry. The second derivatives of the dielectric function are examined through a critical point analysis, allowing us to inspect interband transitions from different points in kW space. The evolution of the band structure over a broad doping range is determined. Specifically, the E1 critical point shifts to higher energies with increased doping of Mn, while all other critical points appear unaffected. The evolution of the critical points results from the interplay between band-gap renormalization due to ionized impurities and sp-d hybridization of the Mn induced impurity band with GaAs valence and conductions bands.