Van der Waals Broken-Gap p-n Heterojunction Tunnel Diode Based on Black Phosphorus and Rhenium Disulfide

The broken-gap (type III) van der Waals heterojunction is of particular interest, as there is no overlap between energy bands of its two stacked materials. Despite several studies on straddling-gap (type I) and staggered-gap (type II) vdW heterojunctions, comprehensive understanding of current transport and optoelectronic effects in a type-III heterojunction remains elusive. Here, we report gate-tunable current rectifying characteristics in a black phosphorus (BP)/rhenium disulfide (ReS₂) type-III p-n heterojunction diode. Current transport in this heterojunction was modeled using the Simmons approximation through direct tunneling and Fowler-Nordheim tunneling in lower- and higher-bias regimes, respectively. We showed that a p-n diode based on a type-III heterojunction is mainly governed by tunneling-mediated transport, but that transport in a type-I p-n heterojunction is dominated by majority carrier diffusion in the higher-bias regime. Upon illumination with a 532 nm wavelength laser, the BP/ReS₂ type-III p-n heterojunction showed a photo responsivity of 8 mA/W at a laser power as high as 100 μW and photovoltaic energy conversion with an external peak quantum efficiency of 0.3%. Finally, we demonstrated a binary inverter consisting of BP p-channel and ReS₂ n-channel thin film transistors for logic applications.