First-principles simulation of monolayer hydrogen passivated Bi₂O₂S₂-metal interfaces

Monolayer (ML) MoS2 is one of the most extensively studied two-dimensional (2D) semiconductors. However, it suffers from low carrier mobility and pervasive Schottky contact with metal electrodes. 2D semiconductor Bi2O2S, a sulfur analogue of 2D Bi2O2Se, has been prepared recently. ML fully hydrogen-passivated Bi2O2S2 (Bi2O2S2H2) posseses a comparable band gap (1.92 eV) with ML MoS2 (1.8 eV), but probably has a better device performance than ML MoS2. Based on the density functional theory, the electron and hole mobilities of ML Bi2O2S2H2 at 300 K are calculated to be 16 447-26 699 and 264-968 cm2 V-1 s-1, respectively. Then we firstly characterize the contact properties of ML half hydrogen-passivated Bi2O2S2 (Bi2O2S2H) with four bulk metal electrodes (Ti, Sc, Pd, and Pt) based on ab initio quantum transport simulation. In the lateral direction, a p-type Schottky contact is found in Pd and Pt electrodes, and the corresponding hole Schottky barrier heights (SBHs) are 0.54 and 0.99 eV, respectively. Remarkably, a coveted n-type Ohmic contact appears in Sc and Ti electrodes. Finally, the current on-off ratio of the ML hydrogen-passivated Bi2O2S2 field effect transistor with a Ti electrode reaches 105. Hence, the good intrinsic properties, contact properties, and large switching ability put ML hydrogen-passivated Bi2O2S2 in the rank of potential channel candidates for post-silicon era field effect transistors.