Reversible Semiconducting-to-Metallic Phase Transition in Chemical Vapor Deposition Grown Monolayer WSe₂ and Applications for Devices

Abstract

Two-dimensional (2D) semiconducting monolayer transition metal dichalcogenides (TMDCs) have stimulated lots of interest because they are direct bandgap materials that have reasonably good mobility values. However, contact between most metals and semiconducting TMDCs like 2H phase WSe₂ are highly resistive, thus degrading the performance of field effect transistors (FETs) fabricated with WSe₂ as active channel materials. Recently, a phase engineering concept of 2D MoS₂ materials was developed, with improved device performance. Here, we applied this method to chemical vapor deposition (CVD) grown monolayer 2H-WSe₂ and demonstrated semiconducting-to-metallic phase transition in atomically thin WSe₂. We have also shown that metallic phase WSe₂ can be converted back to semiconducting phase, demonstrating the reversibility of this phase transition. In addition, we fabricated FETs based on these CVD-grown WSe₂ flakes with phase-engineered metallic 1T-WSe₂ as contact regions and intact semiconducting 2H-WSe₂ as active channel materials. The device performance is substantially improved with metallic phase source/drain electrodes, showing on/off current ratios of 10⁷ and mobilities up to 66 cm²/V·s for monolayer WSe₂. These results further suggest that phase engineering can be a generic strategy to improve device performance for many kinds of 2D TMDC materials