As a member of the group IVB transition metal dichalcogenides (TMDs) family, hafnium disulfide (HfS2) is recently predicted to exhibit higher carrier mobility and higher tunneling current density than group VIB (Mo and W) TMDs. However, the synthesis of high-quality HfS2 crystals, sparsely reported, has greatly hindered the development of this new field. Here, a facile strategy for controlled synthesis of high-quality atomic layered HfS2 crystals by van der Waals epitaxy is reported. Density functional theory calculations are applied to elucidate the systematic epitaxial growth process of the S-edge and Hf-edge. Impressively, the HfS2 back-gate field-effect transistors display a competitive mobility of 7.6 cm2 V−1 s−1 and an ultrahigh on/off ratio exceeding 108. Meanwhile, ultrasensitive near-infrared phototransistors based on the HfS2 crystals (indirect bandgap ≈1.45 eV) exhibit an ultrahigh responsivity exceeding 3.08 × 105 A W−1, which is 109-fold higher than 9 × 10−5 A W−1 obtained from the multilayer MoS2 in near-infrared photodetection. Moreover, an ultrahigh photogain exceeding 4.72 × 105 and an ultrahigh detectivity exceeding 4.01 × 1012 Jones, superior to the vast majority of the reported 2D-materials-based phototransistors, imply a great promise in TMD-based 2D electronic and optoelectronic applications. A facile strategy for the synthesis of high-quality monolayer HfS2 crystals by van der Waals epitaxy is reported. Ultrasensitive near-infrared phototransistors based on the HfS2 crystals exhibit an ultrahigh responsivity 3.08 × 105 A W−1, and an ultrahigh detectivity exceeding 4.01 × 1012 Jones, superior to most 2D materials-based phototransistors.
Published in: "Advanced Materials".