Molybdenum Disulfide Field Effect Transistors under Electron Beam Irradiation and External Electric Fields

Abstract

In this work, monolayer molybdenum disulfide (MoS2) nanosheets, obtained via chemical vapor deposition onto SiO2/Si substrates, are exploited to fabricate field-effect transistors with n-type conduction, high on/off ratio, steep subthreshold slope and good mobility. We study their electric characteristics from 10−6 Torr to atmospheric air pressure. We show that the threshold voltage of the transistor increases with the growing pressure. Moreover, Schottky metal contacts in monolayer molybdenum disulfide (MoS2) field-effect transistors (FETs) are investigated under electron beam irradiation conditions. It is shown that the exposure of Ti/Au source/drain electrodes to an electron beam reduces the contact resistance and improves the transistor performance. It is shown that e-beam irradiation lowers the Schottky barrier at the contacts due to thermally induced atom diffusion and interfacial reactions. The study demonstrates that electron beam irradiation can be effectively used for contact improvement though local annealing. It is also demonstrated that the application of an external field by a metallic nanotip induces a field emission current, which can be modulated by the voltage applied to the Si substrate back-gate. Such a finding, that we attribute to gate-bias lowering of the MoS2 electron affinity, enables a new field-effect transistor based on field emission.