Molybdenum disulfide transistors with enlarged van der Waals gaps at their dielectric interface via oxygen accumulation

Two-dimensional molybdenum disulfide (MoS2) is a potential alternative channel material to silicon for future scaled transistors. Scaling down the gate dielectric and maintaining a high-quality interface is challenging with such materials, because the atomic thickness of MoS2 makes it sensitive to defects common in amorphous gate oxides such as hafnium oxide (HfOx). Here we show that a van der Waals gap of 5.3 & ANGS; can be formed between HfOx and MoS2 via the ozone treatment of a hafnium disulfide (HfS2)/MoS2 stack. The ozone treatment converts the HfS2 flake into a HfOx dielectric, and excess oxygen accumulation at the interface widens the van der Waals gap. Experimental results and density functional theory calculations show that the increased gap decouples the interaction between the HfOx dielectric and MoS2 channel, allowing the intrinsic properties of the MoS2 semiconductor to be preserved. The resulting MoS2 van der Waals-gap-gated transistors exhibit a negligible hysteresis of 10 mV and average subthreshold slope of 63.1 mV dec(-1), which is close to the physical Boltzmann limit of 60.0 mV dec(-1). We also show that the transistors can be used to construct NOT, OR and AND logic gates.