Identifying Grain Boundaries Trap states in Molybdenum Diselenide

Transition metal dichalcogenides in their monolayer form are poised to be a material for next-generation electronics applications owing to their excellent electrical and electronic properties. Single-crystal Molybdenum diselenide (MoSe2) in particular has been shown to have high gate modulation and a current on/off ratio higher than 10⁶ with excellent charge carrier mobility. However, to commercialize such materials, large-scale growth is indispensable, which are not generally single crystalline in nature. Polycrystalline MoSe2 have significant grain boundaries (Gbs) which act as a charge trapping and scattering center leads to limited device performance. While charge scattering is a wide known phenomenon, charge trapping in TMDs relatively unknown. Here, we have investigated the electronic character of MoSe₂ grain boundaries and identified various traps states energy level from first principles. Gb introduces a significant density of deep traps, strongly influencing transport properties. In the conventionally seen Stone-Waals defect structures present at the grain boundaries, the two homoelemental bonds tend to show asymmetry while introducing shallow traps; the Se homoelemental bond presents near conduction band shallow states while Mo homoelemental bond presents near valence band shallow states, such shallow states depending on the homoelemental bond density leads to bandgap broadening. Our work provides new insights on the trap states in low-dimensional materials.