Excitonic emissions from CuInSe₂ on GaAs(001) grown by molecular beam epitaxy

CuInSe₂ epitaxial films grown on (001)-oriented GaAs substrates by molecular beam epitaxy have been characterized by means of low temperature photoluminescence spectroscopy at T=2-102 K. Distinct emission lines were observed near the band gap, and have been investigated further with varying sample temperature. An emission at 1.0386 eV (E_X1) became broader with increasing sample temperature, and still remained up to T=102 K. A distinct, sharp emission at 1.0311 eV (I_X1) which disappeared at a significantly lower temperature than the other peaks was observed only in films with weak donor-related emissions. We attribute such emissions to the ground-state free exciton [FE_n=1] and exciton bound to neutral acceptor [A⁰,X], respectively. The band gap of CuInSe₂ epitaxial films was also determined to be E_g=1.046eV at 2 K using the reported exciton binding energy of E_ex=7 meV.