A comparative study of electrical and opto-electrical properties of a few-layer p-WSe/n-WS heterojunction diode on SiO and h-BN substrates.

Since the innovation of van der Waals heterostructures of 2D materials, the p-n junction diode, a building block of electronics and opto-electronics has been studied in various ways. To date most of them have been studied on SiO or other oxide substrates, although the oxide substrates cause significant degradation of the 2D material's intrinsic properties and device performances. Whereas using hexagonal boron nitride (h-BN) as an underlying layer to the 2D materials is known to preserve their properties. Here we have carefully analyzed the electrical and opto-electrical properties of a p-WSe/n-WS van der Waals heterojunction diode on SiO and the h-BN substrates. Besides the usual enhancement of the field-effect mobility of WSe and WS, we have achieved a significant enhancement of the diode rectification ratio and excellent photovoltaic characteristics on the h-BN substrate. We have obtained more than an order-of-magnitude enhancement of the diode rectification ratio and about two-fold increments in the overall opto-electronics behavior on the h-BN substrate compared with those on the SiO substrate. The values of self-powered photo responsivity and external quantum efficiency are 3 A/W and 588% respectively on the h-BN substrate at 10 mW cm photo-power density and 633 nm wavelength, whereas they reduce to about one-half on the SiO substrate.