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

ABSTRACT

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.