High Mobility WS₂ Transistors Realized by Multilayer Graphene Electrodes and Application to High Responsivity Flexible Photodetectors

The electrical contact is one of the main issues preventing semiconducting 2D materials to fulfill their potential in electronic and optoelectronic devices. To overcome this problem, a new approach is developed here that uses chemical vapor deposition grown multilayer graphene (MLG) sheets as flexible electrodes for WS₂ field-effect transistors. The gate-tunable Fermi level, van der Waals interaction with the WS₂, and the high electrical conductivity of MLG significantly improve the overall performance of the devices. The carrier mobility of single-layer WS₂ increases about a tenfold (50 cm² V⁻¹ s⁻¹ at room temperature) by replacing conventional Ti/Au metal electrodes (5 cm² V⁻¹ s⁻¹) with the MLG electrodes. Further, by replacing the conventional SiO₂ substrate with a thin (1 µm) parylene-C flexible film as insulator, flexible WS₂ photodetectors that are able to sustain multiple bending stress tests without significant performance degradation are realized. The flexible photodetectors exhibited extraordinarily high gate-tunable photoresponsivities, reaching values of 4500 A W⁻¹, and with very short (<2 ms) response time. The work of the heterostacked structure combining WS₂, graphene, and the very thin polymer film will find applications in various flexible electronics, such as wearable high-performance optoelectronics devices.