Photoluminescence excitation spectroscopy of a highly compensated CuGaSe2

The photoluminescence excitation spectra are presented of weakly and highly compensated CuGaSe2, grown under Cu excess and under Cu deficiency, respectively. An overlap is observed between the photoluminescence and the excitation spectrum in the Cu poor material, indicating fluctuating potentials due to high compensation, whereas no overlap is observed in material grown under Cu excess, indicating flat bands. The photoluminescence excitation spectra can be used as measure for the absorption spectrum in the case of flat bands, but not in the case fluctuating potentials, where different emission energies probe different depths of the fluctuations. Methods for the determination of the fluctuation amplitude from the photoluminescence and the excitation spectra are discusse