Deep level transient spectroscopy and theoretical modelling of defect states in few-layer MoS₂

Native defects can essentially affect the properties of semiconductors and devices based on them. The defect influence is critical for 2D materials obtained by mechanical exfoliation from layered crystals, as most defects may be introduced when exfoliating. A film of few-layer MoS₂ flakes on a SiO₂/Si substrate was studied using deep-level transient spectroscopy (DLTS). A set of electron traps with energy levels at 303, 440, and 633 meV below the conduction band was found. The values are compared to those obtained by the density functional theory calculations of most abundant point defects in bilayer MoS₂, such as Mo and S vacancies, Mo+S and S divacancies, or O substituting S in a surface S layer. Based on the calculation results, the three states found by DLTS were attributed to S vacancy (440 meV) and S divacancy (303 and 633 meV), being the most expected when preparing the layered 2D structures by mechanical exfoliation.