Effect of graphene on the photoreflectance and photoluminescence of GaAs

Photoluminescence and photoreflectance spectra of graphene-coated and bare semi-insulating GaAs were taken at 532nm pump excitation. Graphene enhances the photoluminescence of GaAs by a factor of four without modifying the lineshape. Graphene enhances and reverses the sign of the fundamental edge photoreflectance of GaAs. Below the band gap, a minimum is observable in reflectance of graphene coated GaAs at energies lower that the onset of photoluminescence. Considering the lineshape effects in photoreflectance, enhanced photoluminescence may be caused by exciton coupling between photoexcited carriers in graphene and in GaAs.