Ultrafast carrier dynamics and electronic properties of PtSe2/MoSe2 and WSe2 2D TMDC layered structures on mica: combined THz spectroscopy and DFT study

Abstract

A detailed investigation of structure, electronic and optical properties of two transition metal dichalcogenide (TMDC) structures is presented in this study. Sample 1 consists of epitaxially grown bilayer of PtSe₂ (2 monolayers) on MoSe₂ (1 monolayer) deposited on mica substrate – reported here for the first time. Sample 2 comprises a trilayer of WSe₂ grown on mica. The photoconductivities of both samples were characterized using optical pump-terahertz probe spectroscopy under above- and near-bandgap excitations at 400 nm and 800 nm. Both structures exhibit rapid carrier generation and relaxation dynamics, with notable variations depending on excitation wavelength and structures. Complementary density functional theory (DFT) calculations are performed to evaluate the electronic and optical properties of free-standing single layers of MoSe₂, PtSe₂ and WSe₂ and their combined structures corresponding to Sample 1 and Sample 2. The experimental results show strong agreement with calculated band structures. This consistency between experiment and theory underscores the potential of these TMDC structures for future applications in terahertz and high-frequency electronic devices.