Hot-electron relaxation via optical phonon emissions in GaAs/Al_xGa_1-xAs quantum well structures: Dependence upon the alloy composition and barrier width

We present a systematic investigation of the dependence of the hot-electron-optical-phonon interactions on Al composition and barrier width in GaAs/Al_xGa_1-xAs MQW structures. Raman scattering measurements at 15 K are presented for samples with different barrier widths and Al composition. The optical phonon energies emitted by the photoexcited electrons in quantum wells were also determined by using hot-electron-neutral acceptor luminescence techniques. It is shown that the relaxation of hot electrons in the quantum wells is dominated by the GaAs LO phonon emission for small x, but by AlAs-like LO phonons for larger Al composition. For samples with larger barriers, the electrons in the GaAs layer relax mostly through the AlAs-like optical phonon emission. However, in samples with smaller barriers, the relaxation of hot electrons is dominated by the GaAs optical phonon emission.