High-Performance WSe₂ Field-Effect Transistors via Controlled Formation of In-Plane Heterojunctions

Monolayer WSe₂ is a two-dimensional (2D) semiconductor with a direct band gap, and low field-effect mobility is the main constraint preventing WSe₂ from becoming one of the competing channel materials for field-effect transistors (FETs). Here, we report that controlled heating in air significantly improves device performance of WSe₂ FETs in terms of on-state currents and field-effect mobilities. Specifically, after being heated at optimized conditions, chemical vapor deposition grown monolayer WSe₂ FETs showed an average FET mobility of 31 cm²V⁻¹s⁻¹ and on/off current ratios up to 5 × 10⁸. For few-layer WSe₂ FETs, after the same treatment applied, we achieved a high mobility up to 92 cm²V⁻¹s⁻¹. These values are significantly higher than FETs fabricated using as-grown WSe₂ flakes without heating treatment, demonstrating the effectiveness of air heating on the performance improvements of WSe₂ FETs. The underlying chemical processes involved during air heating and the formation of in-plane heterojunctions of WSe₂ and WO_3−x were studied. This work is a step toward controlled modification of the properties of WSe₂ and potentially other TMDCs and may greatly improve device performance for future applications of 2D materials in electronics and optoelectronics.