Coherent phonon oscillations in GaAs/Al/sub x/Ga/sub 1-x/As multiple quantum wells: the x-dependence

摘要: Femtosecond coherent phonon experiments are performed on a series of GaAs/Al/sub x/Ga/sub 1-x/As multiple quantum wells (MQWs) with varying x, at fixed well and barrier width 100 /spl Aring/. For x=0.2, we have found clear beating in time domain. Fourier transformation reveals two distinct peaks the LO TO positions, which is indicative bulk-like plasmon-phonon oscillations growth direction. This surprising, for supposed carrier confinement due to relatively large has been thought forbid such oscillations. At x=0.5, little seen only frequency transformation), agreement earlier results samples x=0.35. Our recent realization existence anomalously well-to-well coupling carriers through thick AlGaAs barriers. In addition, bulk-like, growth-direction oscillation be possible, believe that optical phonons also should able penetrate couple next well. Such propagating model proposed. Finally, our x-dependent studies show more sensitive function x than width.