A comparative study of electrical and opto-electrical properties of a few-layer p-WSe 2 /n-WS 2 heterojunction diode on SiO 2 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 2 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 2 /n-WS 2 van der Waals heterojunction diode on SiO 2 and the h-BN substrates. Besides the usual enhancement of the field-effect mobility of WSe 2 and WS 2 , 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 2 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 -2 photo-power density and 633 nm wavelength, whereas they reduce to about one-half on the SiO 2 substrate.