Ultrafast Dynamic Response of Nanoscale 2D Semiconductor InSe

Terahertz (THz) frequency band has unique advantages, which can be used to study the principle of photo-excited carrier dynamics[1], [2]. It is very important to clarify the potential applications of materials in high-performance electronic and optoelectronic devices. As a traditional layered semiconductor material, indium selenide (InSe) has high carrier mobility and strong optical response and has great development potential in the next generation of electronic and optoelectronic devices[3], [4]. However, due to the diffraction limit of traditional optics, especially in the THz band, the spatial resolution can only reach the micron scale, so it is impossible to directly observe the ultrafast dynamic response of 2D materials at the nanoscale, which limits our access to and cognition of the information of InSe and its nano devices at the micro scale to a certain extent. Here, with the help of THz scattering scanning near-field optical microscopy (THz s-SNOM), we have studied the band gap changes of layered -InSe due to the change of the number of layers in femtosecond time scale and nanometer space scale, and the different carrier responses under laser excitation. This lays an important foundation for the study of InSe and other 2D semiconductor materials and their application in THz devices such as THz ultrafast switches.