Van der Waals Epitaxial Growth of Atomic Layered HfS2 Crystals for Ultrasensitive Near-Infrared Phototransistors

As a member of the group IVB transition metal dichalcogenides (TMDs) family, hafnium disulfide (HfS 2 ) 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 HfS 2 crystals, sparsely reported, has greatly hindered the development of this new field. Here, a facile strategy for controlled synthesis of high-quality atomic layered HfS 2 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 HfS 2 back-gate field-effect transistors display a competitive mobility of 7.6 cm 2 V −1 s −1 and an ultrahigh on/off ratio exceeding 10 8 . Meanwhile, ultrasensitive near-infrared phototransistors based on the HfS 2 crystals (indirect bandgap ≈1.45 eV) exhibit an ultrahigh responsivity exceeding 3.08 × 10 5 A W −1 , which is 10 9 -fold higher than 9 × 10 −5 A W −1 obtained from the multilayer MoS 2 in near-infrared photodetection. Moreover, an ultrahigh photogain exceeding 4.72 × 10 5 and an ultrahigh detectivity exceeding 4.01 × 10 12 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.