Controllable Oxidation for Making Ambipolar or P-type MoOx/MoS2 Transistors

Recently, semiconducting layered materials attract much attention because of prominent potential for making ultrathin body field-effect transistors (FETs). Here, we show controllable oxidation to convert MoS₂ flakes to either ambipolar or p-type FETs. The MoS₂ flakes were heated under ozone exposure for several hours. The surface of oxidized MoS₂ was examined by scanning tunneling microscope. Further, we made FET devices on MoS₂ flakes with thickness less than 30 nm. Before ozone oxidation, the FET devices presented n-type features that are consistent with previous reports. After oxidation, the devices showed Schottky contact properties that were carefully inspected at different bias and gating voltages. The MoS₂ FETs after minor oxidation showed an ambipolar feature and electron transport revealed Mott's 2D variable range hopping. On the other hand, after strong oxidation, the devices presented p-type FET behaviors. The electron transport and transfer characteristics of the p-type FETs were explored as well. From experimental data, we propose a band diagram to explain the oxidation, the formation of MoO_x/MoS₂ heterostructure, and the electron transport behaviors.