Near-zero hysteresis and near-ideal subthreshold swing in h-BN encapsulated single-layer MoS2 field-effect transistors

Abstract

While two-dimensional (2D) van der Waals (vdW) layered materials are promising channel materials for wearable electronics and energy-efficient field-effect transistors (FETs), large hysteresis and large subthreshold swing induced by either dangling bonds at gate oxide dielectrics and/or trap molecules in bubbles at vdW interface are a serious drawback, hampering implementation of the 2D-material based FETs in real electronics. Here, we report a monolayer MoS2 FET with near-zero hysteresis reaching 0.15% of the sweeping range of the gate bias, a record-value observed so far in 2D FETs. This was realized by squeezing the MoS2 channel between top h-BN layer and bottom h-BN gate dielectrics and further removing the trap molecules in bubbles at the vdW interfaces via post-annealing. By segregating the bubbles out to the edge of the channel, we also obtain excellent switching characteristics with a minimum subthreshold swing of 63 mV/dec, an average subthreshold slope of 69 mV/dec for a current range of four orders of magnitude at room temperature, and a high on/off current ratio of 108 at a small operating voltage (<1 V). Such a near-zero hysteresis and a near-ideal subthreshold limit originate from the reduced trap density of ~5.2 × 109 cm−2 eV−1, a thousand times smaller than previously reported values.