Phase-engineered low-resistance contacts for ultrathin MoS₂ transistors

Ultrathin molybdenum disulphide (MoS₂) has emerged as an interesting layered semiconductor because of its finite energy bandgap and the absence of dangling bonds. However, metals deposited on the semiconducting 2H phase usually form high-resistance (0.7 kω μm-10 kω μm) contacts, leading to Schottky-limited transport. In this study, we demonstrate that the metallic 1T phase of MoS₂ can be locally induced on semiconducting 2H phase nanosheets, thus decreasing contact resistances to 200-300 ω μm at zero gate bias. Field-effect transistors (FETs) with 1T phase electrodes fabricated and tested in air exhibit mobility values of ∼50 cm²V^-1s^-1, subthreshold swing values below 100 mV per decade, on/off ratios of >10⁷, drive currents approaching ∼100 μA μm^-1, and excellent current saturation. The deposition of different metals has limited influence on the FET performance, suggesting that the 1T/2H interface controls carrier injection into the channel. An increased reproducibility of the electrical characteristics is also obtained with our strategy based on phase engineering of MoS₂.