PHONON COUPLING ASSOCIATED WITH FREE-TO-BOUND AND BOUND-TO-BOUND TRANSITIONS IN GAAS-LAYERS GROWN BY MOLECULAR-BEAM EPITAXY

The longitudinal-optical- and transverse-optical-phonon modes were obs erved to couple to selective-pair-luminescence transitions in GaAs sam ples. Very little phonon broadening is seen in the phonon-replica tran sitions. This is due to the relatively flat phonon-dispersion curves a t the GAMMA point in k space, where the phonon coupling occurs. Phonon replicas were also observed when the donor-acceptor pairs were resona ntly excited at specific pair separations with the pair impurities bei ng in their ground states. In this excitation, not only was the LO and TO mode coupling to the pump-energy transition observed, but also pho non coupling to the free-to-bound transition. The phonon-coupling ener gy to the free-to-bound transition was determined to be 47.9 meV. The observed phonon-coupling energy is close to the calculated and measure d energy of the local vibrational mode Of Si-28(Ga) in GaAs.