We report the characteristic behaviors of the hysteresis observed in the transfer characteristics of back-gated field-effect transistors with an exfoliated MoS2 channel under various conditions. We find that the hysteresis is strongly enhanced by temperature, environmental gas, or light irradiation. Our measurements reveal the characteristic hysteresis behaviors in a 1 atm oxygen environment, which we explain as an oxygen molecule facilitated charge acceptor on the MoS2 surface. The decrease in the current value in the ON state of the device may indicate that oxygen molecules are more effective charge acceptors than nitrogen molecules. We conclude that intrinsic defects in MoS2, such as S vacancies, which result in effective adsorbate trapping, play an important role in the hysteresis behavior, in addition to oxygen and nitrogen adsorbates on the passivated device surface. The availability of thermally or photo-generated minority carriers (holes) in MoS2 is increased by both light and temperature. This leads to subsequent processes of positive charge trapping, which intensify the hysteresis.
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