Photoelectric properties of pristine and niobium-doped tungsten disulfide layered crystals

Tungsten disulfide (WS2) is a transition-metal dichalcogenide that is suited to next-generation electronic and optoelectronic devices. Doping is necessary for WS2 applications because it allows the inherent characteristics of WS2 to be tuned to increase its functionality. This study determines the effect of niobium (Nb) doping on the photoelectric properties of WS2 crystals. A chemical vapor transport process is used to grow pristine and Nb-doped WS2 crystals. Scanning electron microscopy images show that the WS2 specimens consist of layered crystals. The photoresponsivity of the samples increases as the incident laser power decreases. Nb-doped WS2 crystals are 92 times more photoresponsive than pristine WS2 crystals at a laser power of 2 × 10−8 W. The ratio of the normalized photocurrent for a Nb-doped sample to that for a pristine sample increases as the frequency of the illumination increases to a maximum value of 11.5 at 104 Hz. Time-dependent photocurrent measurements show that the rise and fall times for Nb-doped WS2 crystals are shorter than those for pristine WS2 crystals by at least an order of magnitude. The results of this study show that Nb doping significantly increases the optical response of WS2 crystals.