Liu Wei-Rein, Lin Ja-Hon, Chen Jyun-Sian, Cheng Hsin-Ming, Li Sheng-Jie, Chen Hou-Ren, Hsu Chia-Hung, Hsieh Wen-Feng
National Synchrotron Radiation Research Center Hsinchu 30076 Taiwan
Department of Electro-Optical Engineering, National Taipei University of Technology Taipei 10608 Taiwan
RSC Adv. 2018 Feb 20;8(15):7980-7987. doi: 10.1039/c7ra11702g. eCollection 2018 Feb 19.
Saturation and beating of coherent acoustic phonon (CAP) oscillations were observed and attributed to the screening of a built-in electric field with increasing pump power using degenerate pump-probe measurements near the exciton resonance of polar ZnO/ZnMgO multiple quantum wells (MQWs). After purifying the CAP signals by using an empirical mode decomposition, we found not only that the CAP amplitude follows the trend of the band gap renormalization (BGR) and shows saturation at high pump power, but also that the CAP oscillation period coincides with that of the MQWs, consistent with the XRD and TEM results. An additional low-frequency oscillation modifying the CAP signal is revealed due to the negative change in refractive index caused by BGR as the pump power increases.
通过在极性ZnO/ZnMgO多量子阱（MQW）的激子共振附近使用简并泵浦-探测测量，观察到了相干声子（CAP）振荡的饱和与拍频现象，并将其归因于随着泵浦功率增加，内置电场的屏蔽作用。在使用经验模态分解净化CAP信号后，我们发现不仅CAP振幅遵循带隙重整化（BGR）趋势并在高泵浦功率下呈现饱和，而且CAP振荡周期与MQW的周期一致，这与XRD和TEM结果相符。随着泵浦功率增加，由于BGR导致的折射率负变化，揭示了一种修改CAP信号的额外低频振荡。
