Band-edge photoluminescence of CuGaSe₂ films grown by MBE

Slightly Cu-rich CuGaSe₂ films were grown on [001] oriented GaAs substrates by molecular beam epitaxy. Photoluminescence of the films showed a remarkable emission peaked at 1.71eV at low temperature. It is revealed to be a complex attributable to recombination of free excitons and that of bound excitons. The dissociation energy of free excitons and their localization energy to a center are found to be 16.2meV and 3.3meV, respectively. The band-gap energy, E_g, is estimated to be 1.7310eV at low temperature. It is suggested that the temperature variation of E_g is caused by interaction with phonons of 26meV which corresponds to the mean value of optical phonons.