OPTICAL-PHONON EMISSION IN GAAS ALAS MULTPLE-QUANTUM-WELL STRUCTURES DETERMINED BY HOT-ELECTRON LUMINESCENCE/

We have performed hot-electron photoluminescence experiments on a numb er of different Be-doped GaAs/AlAs multiple-quantum-well structures (M QW's), with fixed well width of 40 Angstrom and barrier thicknesses be tween 5 and 80 Angstrom, in order to determine the energy of the optic al phonons emitted by the hot electrons before recombination with the acceptor levels of the GaAs quantum wells. A continuum theory of optic al phonons in GaAs/AlAs multiple quantum wells was used to estimate th e effective energy of the optical phonons emitted during the hot-elect ron energy relaxation. The theoretical calculations are compared with the energy separation of the measured hot photoluminescence peaks and a detailed analysis of the different modes contributing to the energy relaxation is performed. For MQW's with large barriers, i.e., 40-Angst rom GaAs and 80 Angstrom AlAs, the energy relaxation is dominated by t he AlAs phonons. However, for samples with smaller barrier widths, i.e ., 40-Angstrom GaAs and either 5- or 10-Angstrom AlAs, relaxation via the emission of GaAs modes is more important. Nevertheless, relaxation by AlAs phonons is still significant producing an effective energy se paration of the hot photoluminescence peaks between that of the pure G aAs and the AlAs MQW optical-phonon energies.