Investigation of ultrafast photocurrents in two-dimensional transition metal dichalcogenides after femtosecond laser pulse excitation

The discovery of graphene and its unique properties has drawn attention of scientists to the other two-dimensional (2D) materials. They possess properties necessary for the next generation optoelectronic devices such as photovoltaics, LEDs, photodetectors, phototransistors and others. Due to spatial confinement, the electron mobilities in these materials are high, while the band structure itself can be adjusted by stacking atomic layers. This, in turn, introduces the universal applications throughout a wide range of electromagnetic spectrum and, generally, to technological industry. The 2D transition metal dichalcogenides (TMD) are new and comprehensively studied materials in scientific community. In the present study, many-layer and single-layer MoSe2, MoS2 and WSe2 materials would be characterized by terahertz (THz) excitation spectra, carrier lifetimes and other optical and electronic properties. The investigations would allow determining the most important physical parameters of these materials and suggest their potential applications.

Our laboratory has five femtosecond pulse lasers, one of which is the amplified 200 kHz repetition rate system with an optical parametric amplifier (OPA) capable of tuning laser wavelength in a 640 to 2500 nm range. This system allows us to characterize the band structure of semiconducting materials by registering THz waves emitted by the ultrafast photocurrents. We have expertise in the optical pump – THz probe method investigating the carrier dynamics within a few hundred picosecond range, as well as estimating the carrier mobility. We have a commercial THz spectrometer (0,1 – 5 THz), which we use to determine phonon frequencies and/or plasma frequencies. In addition, we are installing a THz ellipsometry system, which will provide an alternative contactless method to estimate the carrier mobility.
For more information, please contact the theme supervisor A. Krotkus.