Raman and hot electron-neutral acceptor luminescence studies of electron-optical phonon interactions in GaAs/Al_xGa_1-xAs quantum wells

Using two optical techniques, we have measured the Frohlich interactions between electrons and optical phonons on a number of different Be-doped GaAs/Al_xGa_1-xAs multiple quantum well structures. Raman scattering measurements at 15 K are presented for GaAs/Al_xGa_1-xAs quantum wells with Al compositions of x = 0.3,0.5,0.7 and 1.0. And also for GaAs/AlAs, GaAs/Al_0.7Ga_0.3As with fixed well width of 50 angstroms and barrier with between 5 to 120 angstroms. The GaAs-like and AlAs-like phonon frequencies of the first-order modes are measured as a function of Al composition and barrier widths. We have also performed hot electron - neutral acceptor luminescence in order to determine average optical phonon energies emitted by the photoexcited electrons in quantum wells with the acceptor levels of the GaAs wells. It is shown that the relaxation of hot electrons in the GaAs/Al_xGa_1-xAs quantum wells is dominated by the GaAs LO phonon emission for small x, but by AlAs-like LO phonons for larger Al compositions. For the quantum wells with largest barrier width investigated, the average energy of the emitted LO phonon is close to the AlAs LO phonon mode. At a barrier width of 5 angstroms, the energy of emitted LO phonon decreases to a value close to the GaAs LO phonons, nevertheless, there is still a significant contribution from the emission of AlAs-like modes.