Influence of Mn, Fe, Co, and Cu Doping on the Photoelectric Properties of 1T HfS Crystals.

Doping plays a vital role in the application of transition-metal dichalcogenides (TMDCs) because it can increase the functionality of TMDCs by tuning their native characteristics. In this study, the influence of Mn, Fe, Co, and Cu doping on the photoelectric properties of HfS was investigated. Pristine, Mn-, Fe-, Co-, and Cu-doped HfS crystals were grown using the chemical vapor transport method. Scanning electron microscopy images showed that the crystals were layered and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy measurements confirmed that the crystals were in the 1T-phase with a CdI-like structure. The bandgap of pristine HfS obtained from the absorption and photoconductivity spectra was approximately 1.99 eV. As the dopant changed from Mn, Fe, and Co, to Cu, the bandgap gradually increased. The activation energies of the samples were determined using temperature-dependent current-voltage curves. After doping, the activation energy decreased, and the Co-doped HfS exhibited the smallest activation energy. Time-resolved photoresponse measurements showed that doping improved the response of HfS to light; the Co-doped HfS exhibited the best response. The photoresponsivity of HfS as a function of the laser power and bias voltage was measured. After doping, the photoresponsivity increased markedly; the Co-doped HfS exhibited the highest photoresponsivity. All the experimental results indicated that doping with Mn, Fe, Co, and Cu significantly improved the photoresponsive performance of HfS, of which Co-doped HfS had the best performance.