Few-layer HfS2 transistors

HfS₂ is the novel transition metal dichalcogenide, which has not been experimentally investigated as the material for electron devices. As per the theoretical calculations, HfS₂ has the potential for well-balanced mobility (1,800 cm²/V·s) and bandgap (1.2 eV) and hence it can be a good candidate for realizing low-power devices. In this paper, the fundamental properties of few-layer HfS₂ flakes were experimentally evaluated. Micromechanical exfoliation using scotch tape extracted atomically thin HfS₂ flakes with varying colour contrasts associated with the number of layers and resonant Raman peaks. We demonstrated the I-V characteristics of the back-gated few-layer (3.8 nm) HfS₂ transistor with the robust current saturation. The on/off ratio was more than 10⁴ and the maximum drain current of 0.2 μA/μm was observed. Moreover, using the electric double-layer gate structure with LiClO₄:PEO electrolyte, the drain current of the HfS₂ transistor significantly increased to 0.75 mA/μm and the mobility was estimated to be 45 cm²/V·s at least. This improved current seemed to indicate superior intrinsic properties of HfS₂. These results provides the basic information for the experimental researches of electron devices based on HfS₂.