Studies of Sub-THz Acoustic Attenuations in GaN by using acoustic transducer with double quantum wells
Fan Jun Wei1*, Jinn-Kong Sheu2, Kung-Hsuan Lin1
1Physics, Academia Sinica, Taipei, Taiwan
2Photonics, National Cheng Kung University, Tainan, Taiwan
* presenting author:樊君偉,
In recent ten years, InGaN/GaN heterostructures have been used to efficiently generate and detect coherent acoustic waves between 100GHz and 2 THz. They have been utilized to study sub-THz acoustic properties of materials such as silica[1][2] and ice[3]. By using single quantum well structure as the acoustic transducer, broad band acoustic spectra can be obtained in single pump-probe trace. However, the acoustic signal initiated in the single quantum well by the femtosecond optical pulses is usually embedded in the transient electronic signals at around zero time-delay. For acoustic analysis, the acoustic energy excited within the acoustic transducer is an important parameter.
In this presentation, we demonstrate how to use double quantum well structure as the acoustic transducer to study acoustic attenuations in GaN cap layer. Several mechanisms such as interface roughness, defect scattering, and anharmonic phonon decay can contribute to acoustic attenuations in GaN. We have done temperature-dependent studies from 100 K to 300 K to investigate different acoustic attenuation mechanisms in GaN in sub-THz regime. This technique can also be applied to study other materials such as glass and glass-forming liquid on the top of the GaN cap layer.

Keywords: THz acoustics, acoustic transducer, acoustic attenuation, InGaN/GaN heterostructures