A Se vacancy induced localized Raman mode in two-dimensional MoSe2 grown by CVD

Abstract

Defects play a significant role in optical properties of semiconducting two-dimensional transition metal dichalcogenides (TMDCs). In ultra-thin MoSe2, a remarkable feature at ~250 cm-1 in Raman spectra is ascribed to be a defect-related mode. Recent attempts failed to explain the origin of this peak, leaving it being a mystery. Here in this work, we demonstrate that this peak is a Se vacancy induced defect mode. Heat effect and hydrogen etching are two main factors to introduce Se vacancies in CVD process of growing MoSe2. A phonon confinement model can well explain the behaviors of intrinsic Raman modes. Density functional theory (DFT) calculation reveals that single Se vacancy (VSe) is responsible for the appearance of Raman peak at ~250 cm-1 and this mode is an A1g-like localized mode which is also confirmed by polarized Raman scattering experiment. The relative strength of this mode can be a characterization of the quality of 2D MoSe2. This work may offer a simple method to tailor chalcogenide vacancies in 2D TMDCs and provide a way to study their vibrational properties.

References in corpus (9)

• Atomically thin MoS2: A new direct-gap semiconductor
• Valley polarization in MoS2 monolayers by optical pumping
• Two-dimensional transition metal dichalcogenides under electron irradiation: defect production and doping
• Acoustic phonon limited mobility in two-dimensional semiconductors: Deformation potential and piezoelectric scattering in monolayer MoS2 from first principles
• Control of Radiation Damage in MoS2 by Graphene Encapsulation
• Resonance effects in the Raman scattering of mono- and few layers MoSe${}_2$
• Davydov splitting and excitonic resonance effects in Raman spectra of few-Layer MoSe2
• Ambipolar Light-Emitting Transistors on Chemical Vapor Deposited Monolayer MoS2
• Probing the uniaxial strains in MoS${}_2$ using polarized Raman spectroscopy: A first-principles study