Tuning the threshold voltage of MoS2 field-effect transistors via surface treatment

Abstract

Controlling the threshold voltage (V_th) of a field-effect transistor is important for realizing robust logic circuits. Here, we report a facile approach to achieve bidirectional V_th tuning of molybdenum disulfide (MoS₂) field-effect transistors. By increasing and decreasing the amount of sulfur vacancies in the MoS₂ surface, the V_th of MoS₂ transistors can be left- and right-shifted, respectively. Transistors fabricated on perfect MoS₂ flakes are found to exhibit a two-fold enhancement in mobility and a very positive V_th (18.5 ± 7.5 V). More importantly, our elegant hydrogen treatment is able to tune the large V_th to a small value (∼0 V) without any performance degradation simply by reducing the atomic ratio of S : Mo slightly; in other words, it creates a certain amount of sulfur vacancies in the MoS₂ surface, which generate defect states in the band gap of MoS₂ that mediates conduction of a MoS₂ transistor in the subthreshold regime. First-principles calculations further indicate that the defect band's edge and width can be tuned according to the vacancy density. This work not only demonstrates for the first time the ease of tuning the V_th of MoS₂ transistors, but also offers a process technology solution that is critical for further development of MoS₂ as a mainstream electronic material.