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

Abstract

As a member of the group IVB transition metal dichalcogenides (TMDs) family, hafnium disulfide (HfS ) 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 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 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 back-gate field-effect transistors display a competitive mobility of 7.6 cm V s and an ultrahigh on/off ratio exceeding 10 . Meanwhile, ultrasensitive near-infrared phototransistors based on the HfS crystals (indirect bandgap ≈1.45 eV) exhibit an ultrahigh responsivity exceeding 3.08 × 10 A W , which is 10 -fold higher than 9 × 10 A W obtained from the multilayer MoS in near-infrared photodetection. Moreover, an ultrahigh photogain exceeding 4.72 × 10 and an ultrahigh detectivity exceeding 4.01 × 10 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.

Sub‐Millimeter‐Scale Monolayer p‐Type H‐Phase VS2

“…[ 19 ] The mica substrate plays an important role in the synthesis process for its high thermal stability, excellent chemical inertness, and free of dangling bonds which facilitate the van der Waals epitaxial growth regardless of the lattice mismatch. [ 20,21 ] Due to the weak van der Waals interaction between VS 2 and mica substrate, it is easy to transfer the as‐synthesized material to arbitrary substrates, such as SiO 2 /Si substrate, as shown in Figure 1e and Figure S1, Supporting Information. Atomic force microscope (AFM) was employed to determine the thickness of VS 2 nanosheet, and the step height of ≈0.6 nm demonstrates that the as‐synthesized products are monolayer (Figure 1f).…”

2D Metal Chalcogenides for IR Photodetection

“…As shown in Figure c, the HfS 2 phototransistor exhibits an ultrahigh responsivity in excess of 3.08 × 10 5 A W −1 , ultrahigh photogain exceeding 4.72 × 10 5 , and ultrahigh detectivity over 4 × 10 12 Jones, which is superior to the vast majority of the reported 2D TMDs‐based IR phototransistors . Such outstanding performance might be attributed to the high crystal quality and superior field effect transistor properties of a competitive mobility of 7.6 cm 2 V −1 s −1 and an ultrahigh on/off ratio exceeding 10 8 , which minimize the defect density, the deleterious effects of defects and trap states, and facilitate photogenerated carriers transport in the HfS 2 channel . More recently, the 2D noble metal dichalcogenides PtSe 2 is also emerging in IR photodetection .…”

“…Abnormally, a large anomalous current emerged in the Td‐WTe 2 photodetector at the illumination of 3.8 µm due to light‐induced surface bandgap opening . Meanwhile, as an another important member of the 2D TMDs family, 2D HfS 2 (indirect bandgap ≈ 1.45 eV) shows remarkable optical response in IR detection . As shown in Figure c, the HfS 2 phototransistor exhibits an ultrahigh responsivity in excess of 3.08 × 10 5 A W −1 , ultrahigh photogain exceeding 4.72 × 10 5 , and ultrahigh detectivity over 4 × 10 12 Jones, which is superior to the vast majority of the reported 2D TMDs‐based IR phototransistors .…”

“…Inset shows the 3D schematic of the HfS 2 phototransistor. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Flexible Photodetector Based on 2D Materials: Processing, Architectures, and Applications

“…Recently HfS 2 has started being explored as an alternative to MoS 2 and WSe 2 due to its superior carrier mobility up to 1800 cm 2 V −1 s −1 and current density 100 times higher than that of MoS 2 . Wang et al demonstrate for the first time an HfS 2 photodetector in PET substrate .…”