Effect of temperature–bias annealing on the hysteresis and subthreshold behavior of multilayer MoS2 transistors

The transfer characteristics (ID–VG) of multilayers MoS2 transistors with a SiO2/Si backgate and Ni source/drain contacts have been measured on as-prepared devices and after annealing at different temperatures (Tann from 150 °C to 200 °C) under a positive bias ramp (VG from 0 V to +20 V). Larger Tann resulted in a reduced hysteresis of the ID–VG curves (from ∼11 V in the as-prepared sample to ∼2.5 V after Tann at 200 °C). The field effect mobility (∼30 cm2 V–1 s–1) remained almost unchanged after the annealing. On the contrary, the subthreshold characteristics changed from the common n-type behaviour in the as-prepared device to the appearance of a low current hole inversion branch after annealing. This latter effect indicates a modification of the Ni/MoS2 contact that can be explained by the formation of a low density of regions with reduced Schottky barrier height (SBH) for holes embedded in a background with low SBH for electrons. Furthermore, a temperature dependent analysis of the subthreshold characteristics revealed a reduction of the interface traps density from ∼9 × 1011 eV–1cm–2in the as-prepared device to ∼2 × 1011 eV–1cm–2after the 200 °C temperature–bias annealing, which is consistent with the observed hysteresis reduction. (Figure presented.) Schematic representation of a back-gated multilayer MoS2 field effect transistor (left) and transfer characteristics (right) measured at 25 °C on an as-prepared device and after the temperature–bias annealing at 200 °C under a positive gate bias ramp from 0 V to +20 V.