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 (n_c) is sensitive to impurity density (n_i) 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).