Van der Waals Epitaxial Growth of Atomic Layered HfS 2 Crystals for Ultrasensitive Near-Infrared Phototransistors.

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.