Modification of contacts and channel properties in two-dimensional field-effect transistors by 10 keV electron beam irradiation

Abstract

We report a systematic electrical characterization of Mos2 and PdSe2 based FETs, with Ti/Au and Pd/Au contacts respectively, to investigate the effect of electron beam irradiation on the transistor channel current, threshold voltage, and contact resistance. We use a 10 keV electron beam inside a scanning electron microscope to irradiate the channel and/or the contact regions of the transistors and perform in-situ electrical measurements profiting of high precision metallic nanoprobes working as the source and the drain contacts. For Mos2 based devices, we investigate the effect of electron irradiation either on the contact region or on the channel regions. Irradiation of the contact region causes an improvement of the transistor conduction by lowering the contact resistance, which we explain in terms of Schottky barrier reduction at the metal/Moxa interfaces. The irradiation with fluence below 100 e−/nm2 on Mos2 channel region increases the device conductance and shifts the threshold voltage towards more negative voltages. For PdS2 based devices, electron beam irradiation with larger fluence up to 4200 e−/nm2 is detrimental to the conduction properties of the device, causing modification of the conduction from n-type to p-type, likely due to the accumulation of negative charges at the Si/SiO2 interface. Moreover, charge carrier mobility is reduced by the formation of defects both in the PdSe2 nanosheets and at the Si/Si02 interface.