Research on the Photoelectric Properties of HfS₂ under High Pressure

HfS₂, as a typical IVB group transition metal dichalcogenide (TMDs) material, has shown great potential in various fields such as photo-sensing, communication, and imaging due to its high carrier mobility and interlayer current density characteristics. Recent studies have revealed the significant role of pressure in modulating the spectral response range and electrical transport properties of TMDs, which has sparked our interest in studying the pressure regulation of the optoelectronic properties of HfS₂. In this study, we have performed diamond anvil cell based high-pressure in-situ photocurrent, Raman scattering spectroscopy, alternating current impedance spectroscopy, and ultraviolet-visible absorption spectroscopy measurements, and combined first-principles calculations to systematically investigate the effects of pressure on the electrical transport and optoelectronic properties of HfS₂. The experimental results showed that the photocurrent of HfS₂ continuously increased with pressure. Within the pressure range of 0-10.2 GPa, the photocurrent and response of HfS₂ show a rapid upward trend with increasing pressure; at 10.2 GPa, the photocurrent and response of HfS₂ (Iph = 0.32 μA, R = 8.19 μA/W) are about three orders of magnitude higher than the initial values at 0.5 GPa (Iph = 1.40×10⁻⁴ μA, R = 3.56×10⁻³ μA/W). At the pressure above 10.2 GPa, the growth rate of photocurrent and response slow down significantly, which is related to the structural phase transition of HfS₂ near 10.0 GPa. Further compression to 30.1 GPa results in a maximum photocurrent of 3.35 μA, which was five orders of magnitude higher than the initial value at 0.5 GPa. This significant enhancement is attributed to the strengthening of S-S interlayer interaction forces under pressure, which leads to a decrease in band gap and resistivity. In addition, we use the WIEN2k software package, based on the modified Becke-Johnson (mBJ) exchange-correlation potential, to calculate and analyze the electronic band structure and optical properties of HfS₂ in its initial phase. The calculation results have shown that with increasing pressure, the optical absorption coefficient and the real part of the photoconductivity of HfS₂ along the c-axis significantly increased, further revealing the intrinsic physical mechanism of the enhanced photoresponse of HfS₂ under pressure. This study provides a new approach for pressure regulation of the optoelectronic properties of layered materials.