Charge Neutral MoS2 Field Effect Transistors Through Oxygen Plasma Treatment

TL;DR

This study demonstrates that oxygen plasma treatment effectively passivates defects in MoS2 transistors, restoring charge neutrality, shifting threshold voltage near zero, increasing mobility significantly, and reducing device variability for improved practical application.

Contribution

The paper introduces a simple oxygen plasma process that passivates surface defects in MoS2 transistors, enhancing performance and uniformity compared to untreated devices.

Findings

Threshold voltage shifted from -18.7V to -0.9V

Mobility increased up to 190-fold

Device-to-device variability was significantly reduced

Abstract

Lithographically fabricated MoS2 field effect transistors suffer from several critical imperfections, including low sub-threshold swings, large turn-on gate voltages (VT), and wide device-to-device variability. The large magnitude and variability of VT 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 cites, such as S vacancies, and surface contamination. This plasma treatment restores charge neutrality to the MoS2 and shifts the threshold turn-on voltage towards 0V. Out of the 8 devices measured, all exhibit a shift of the FET turn-on voltage from an average of -18.7V to -0.9V. The oxygen plasma treatment passivates these defects, which reduces surface scattering, causing increased mobility and improved subthreshold swing. For as-prepared devices with low mobilities (~0.01cm2/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.