Thickness-dependent excitonic properties of atomically thin 2H-MoTe2*

Abstract

Two-dimensional (2D) 2H-MoTe2 is a promising semiconductor because of its small bandgap, strong absorption, and low thermal conductivity. In this paper, we systematically study the optical and excitonic properties of atomically thin 2H-MoTe2 (1–5 layers). Due to the fact that the optical contrast and Raman spectra of 2H-MoTe2 with different thicknesses exhibit distinctly different behaviors, we establish a quantitative method by using optical images and Raman spectra to directly identify the layers of 2H-MoTe2 thin films. Besides, excitonic states and binding energy in monolayer/bilayer 2H-MoTe2 are measured by temperature-dependent photoluminescence (PL) spectroscopy. At temperature T = 3.3 K, we can observe an exciton emission at ∼ 1.19 eV and trion emission at ∼ 1.16 eV for monolayer 2H-MoTe2. While at room temperature, the exciton emission and trion emission both disappear for their small binding energy. We determine the exciton binding energy to be 185 meV (179 meV), trion binding energy to be 20 meV (18 meV) for the monolayer (bilayer) 2H-MoTe2. The thoroughly studies of the excitonic states in atomically thin 2H-MoTe2 will provide guidance for future practical applications.