Intrinsic magneto-optical spectra of GaMnAs

In the spectrum of reflection magnetic circular dichroism (MCD) of Ga_1−xMn_xAs, the E₀ peak energy, which is assigned to the band gap of GaMnAs, is higher than the band gap energy of GaAs. In the past, this blue shift was attributed to the Moss-Burstein effect, in which the Fermi level moves toward lower energy in the valence band as the Mn concentration x increases; however, this picture is inconsistent with the impurity-band conduction picture, which has been verified in recent studies. Here, by measuring reflection MCD spectra of Ga_1−xMn_xAs thin films (x = 1%, 2%, and 8%) with various thicknesses, we derive the off-diagonal element of the dielectric tensor of GaMnAs and obtain the intrinsic MCD spectra of GaMnAs that are free from optical interference. We find that optical interference is significantly strong even in the extremely thin (10–100 nm) GaMnAs films and that the E₀ peak of the intrinsic MCD spectra is located close to the band gap energy of GaAs even in highly Mn-doped GaMnAs. This is consistent with the recent understanding of the band structure of GaMnAs; the Fermi level exists in the impurity band in the band gap regardless of x.