A comparative study of electrical and opto-electrical properties of a few-layer p-WSe2/n-WS2 heterojunction diode on SiO2 and h-BN substrates

Abstract

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 SiO₂ 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-WSe₂/n-WS₂ van der Waals heterojunction diode on SiO₂ and the h-BN substrates. Besides the usual enhancement of the field-effect mobility of WSe₂ and WS₂, 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 SiO₂ 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 SiO₂ substrate.