The growth mechanism and intriguing optical and electronic properties of few-layered HfS₂

Due to electronic properties superior to group VIB (Mo and W) transition metal dichalcogenides (TMDs), group IVB (Hf and Zr) TMDs have become intriguing materials in next-generation nanoelectronics. Therefore, the growth of few-layered hafnium disulfide (HfS₂) on c-plane sapphire as well as on a SiO₂/Si substrate has been demonstrated using chemical vapour deposition (CVD). The structural properties of HfS₂ were investigated by recording X-ray diffraction patterns and Raman spectra. The XRD results reveal that the layers are well oriented along the (0001) direction and exhibit the high crystalline quality of HfS₂. The Raman spectra confirm the in-plane and out-plane vibration of Hf and S atoms. Moreover, the HfS₂ layers exhibit strong absorption in the UV to visible region. The HfS₂ layer-based photodetector shows a photoresponsivity of ∼1.6, ∼0.38, and ∼0.21 μA W^-1 corresponding to 9, 38, and 68 mW cm^-2, respectively under green light illumination and is attributed to the generation of a large number of electron-hole pairs in the active region of the device. Besides, it also exhibits the highly crystalline structure of HfS₂ at high deposition temperature. The PL spectrum shows a single peak at ∼1.8 eV and is consistent with the pristine indirect bandgap of HfS₂ (∼2 eV). Furthermore, a few layered HfS₂ back gate field-effect transistor (FET) is fabricated based on directly grown HfS₂ on SiO₂/Si, and the device exhibits p-type behaviour. Thus, the controllable and easy growth method opens the latest pathway to synthesize few layered HfS₂ on different substrates for various electronic and optoelectronic devices.