Transport properties of two-dimensional MoSe2 and its application to high-performing all-2D photodetector

The transport properties of two-dimensional (2D) molybdenum diselenide (MoSe2) were comprehensively investigated. To understand experimental data, a detailed transport theory was developed by considering charged impurity, acoustic phonon, and optical phonon scatterings, and excellent quantitative agreements were obtained between theory and experiment. The observed metal-insulator transition (MIT) in MoSe2 is attributed to the screened Coulombic disorder arising from the random distribution of charged impurities in the semiconductor structures, indicating that MoSe2 2D MIT is a finite-temperature density-inhomogeneity-driven effective transition. We argue that the critical carrier density (nc) is sensitive to impurity density (ni) as a result of the competition with intrinsic phonons. Due to low impurity density, our devices show linear ohmic contact between the channel and electrodes. Furthermore, high performance MoSe2 all-2D photodetectors are fabricated by using a transparent electrode on a hexagonal boron nitride (hBN) substrate. The fabricated all-2D MoSe2 photodetectors demonstrate a substantial enhancement of photocurrent due to multiple reflections at the hBN and MoSe2 interface. Additionally, they exhibit a high photo-to-dark current ratio (1.1 ​× ​104), high responsivity (3500 A/W), and high detectivity (5.8 ​× ​1010 Jones).