Metal–Insulator Transition Driven by Traps in 2D WSe₂ Field‐Effect Transistor

Abstract

Abstract Localized trap density ( D t ) at the 2D channel–gate dielectric interface and its relative strength to carrier–carrier interactions depending on the thickness of the 2D channel can determine the nature of a metal–insulator transition (MIT) in 2D materials. Here, the MIT occurring in WSe 2 devices is systematically analyzed by varying the WSe 2 thickness from ≈20 nm to monolayer to explore the effects of D t on MIT. The corresponding critical carrier density increases from ≈8.30 × 10 11 to 9.45 × 10 12 cm –2 and D t from ≈6.02 × 10 11 to 1.13 × 10 13 cm –2 eV –1 as WSe 2 thickness decreases from ≈20 nm to monolayer. These large increments in D t with decreasing thickness of WSe 2 induce a strong potential fluctuation in the band of WSe 2 , causing charge density inhomogeneity in the system, which attributed to tuning the MIT. The critical percolation exponent is strongly dependent on WSe 2 thickness with an excellent agreement between the transport data and percolation theory achieved from thinner WSe 2 devices, while the transport data measured from multilayer WSe 2 devices does not obey the percolation theory. These results suggest that the nature of MIT strongly depends on the WSe 2 channel thickness and corresponding unscreened charge impurity and strength of D t at the interface.