Charge neutral MoS_2 field effect transistors through oxygen plasma treatment

摘要

Lithographically fabricated MoS_2 field effect transistors suffer from several critical imperfections, including low sub-threshold swings, large turn-on gate voltages (V_T), and wide device-to-device variability. The large magnitude and variability of V_T stems from unclean interfaces, trapped charges in the underlying substrate, and sulfur vacancies created during the mechanical exfoliation process. In this study, we demonstrate a simple and reliable oxygen plasma treatment, which mitigates the effects of unintentional doping created by surface defect sites, such as S vacancies, and surface contamination. This plasma treatment restores charge neutrality to the M0S2 and shifts the threshold turn-on voltage towards 0 V. Out of the 10 devices measured, all exhibit a shift of the FET turn-on voltage from an average of -18 V to -2 V. The oxygen plasma treatment passivates these defects, which reduces surface scattering, causing increased mobility and improved sub-threshold swing. For as-prepared devices with low mobilities (～0.01 cm~2/V s), we observe up to a 190-fold increase in mobility after exposure to the oxygen plasma. Perhaps the most important aspect of this oxygen plasma treatment is that it reduces the device-to-device variability, which is a crucial factor in realizing any practical application of these devices.