MoS₂/Si and WS₂/Si 2D/3D heterojunction photodiodes fabricated by low-temperature plasma enhanced CVD

We prepared MoS₂ and WS₂ tri-layers directly on Si substrates using atmospheric-pressure plasma enhanced chemical vapor deposition (AP-PECVD). High pressure (over 100 Torr) plasma formation and low-temperature (under 200°C) growth of AP-PECVD enabled high-quality 2D/3D semiconductor (SC) heterojunctions on a large area (over 4 inch) at a high deposition rate (10 minutes for 2 inch). The fabricated devices showed clear rectifying behaviors and large shunt resistance, indicating formation of uniform heterojunction diodes. Relatively large dark current of the heterojunctions under reverse bias could be attributed to band-to-band tunneling and avalanche multiplication process. Temperature dependence of ideality factor was studied to understand the major recombination processes, based on the conventional 3D SC model. Both of the MoS₂/Si and WS₂/Si heterojunctions exhibited large and fast photocurrent responses to the laser illumination (wavelength: 532 nm). The measured photocurrent was linear to the laser power, indicating interfacial defect states could not suppress photo-generated carrier collection. All the results demonstrated high quality 2D/3D SC heterojunction photodiodes with clean interfaces were prepared by AP-PECVD.