Ultrathin Semiconducting Bi₂Te₂S and Bi₂Te₂Se with High Electron Mobilities

Abstract

High\ncarrier mobility and moderate band gap are two key properties\nof electronic device applications. Two ultrathin two-dimensional (2D)\nsemiconductors, namely, Bi₂Te₂S and Bi₂Te₂Se nanosheets, with novel electronic and optical properties\nare predicted based on first-principles calculations. The Bi₂Te₂S and Bi₂Te₂Se monolayers own\nmoderate band gaps (∼0.7 eV) and high electron mobilities (∼20 000\ncm² V^–1 s^–1), and they\ncan absorb sunlight efficiently through the whole incident solar spectrum.\nMeanwhile, layer-dependent exponential decay band gaps are also unveiled.\nThe relatively low interlayer binding energies suggest that these\nmonolayers can be easily exfoliated from bulk structures. Their high\ndynamical and thermal stabilities are further verified by phonon dispersion\ncalculations and ab initio molecular dynamics simulations. The exceptional\nproperties render Bi₂Te₂X (X = S, Se) monolayers\npromising candidates in future high-speed (opto)­electronic devices.