https://www.sciencedaily.com/releases/2021/05/210510104336.htm > Terahertz (THz) waves can be generated by ultrafast processes occurring in a material. By looking at THz emission, researchers have been able to study different processes at the quantum level -- from simple bulk semiconductors to advanced quantum materials such as multiple quantum wells . > The THz research group led by Prof. Masayoshi Tonouchi at the Institute of Laser Engineering, Osaka University and his PhD student Abdul Mannan, together with international collaborators Prof. Dmitry Turchinovich at Bielefeld University and Prof. Andreas Hangleiter at Technical University of Braunschweig, has measured multifunction response in buried GaInN/GaN multiple quantum wells (MQWs) which includes dynamic screening effect of the built-in field inside the GaInN quantum wells, capacitive charge oscillation between GaN and GaInN quantum wells, and acoustic wave beams launched by the stress release between GaN and GaInN. All these functions can be monitored by observing THz emission into free space. In addition, it was proven that the propagating acoustic waves provide a new technique to evaluate the thickness of buried structure in devices at the resolution of 10 nm on the wafer scale, making nano-seismology a unique LTEM application for wide-bandgap quantum devices.