Bandgap narrowing in Mn doped GaAs probed by room-temperature photoluminescence

The electronic band structure of the (Ga,Mn)As system has been one of the most intriguing problems in solid state physics over the past two decades. Determination of the band structure evolution with increasing Mn concentration is a key issue to understand the origin of ferromagnetism. Here, we present room-temperature photoluminescence and ellipsometry measurements of $\mathrm{G}{\mathrm{a}}_{100%\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}\mathrm{As}$ alloy. The upshift of the valence band is proven by the redshift of the room temperature near band-gap emission from the $\mathrm{G}{\mathrm{a}}_{100%\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}\mathrm{As}$ alloy with increasing Mn content. It is shown that even a doping by 0.02% of Mn affects the valence-band edge, and it merges with the impurity band for a Mn concentration as low as 0.6%. Both x-ray diffraction pattern and high-resolution cross-sectional transmission electron microscopy images confirmed full recrystallization of the implanted layer and GaMnAs alloy formation.