Atomically Controlled Tunable Doping in High‐Performance WSe2 Devices

• Published in: Advanced electronic materials Vol. 6; no. 8
• Main Authors: Pang, Chin‐Sheng, Hung, Terry Y. T., Khosravi, Ava, Addou, Rafik, Wang, Qingxiao, Kim, Moon J., Wallace, Robert M., Chen, Zhihong
• Format: Journal Article
• Language: English
• Published: 01.08.2020
• Subjects: 2D materials; atomically layered control; contact resistance; field‐effect transistors; tunable doping
• ISSN: 2199-160X; 2199-160X
• DOI: 10.1002/aelm.201901304

2D transitional metal dichalcogenide (TMD) field‐effect transistors are promising candidates for future electronic applications, owing to their potential for ultimate device scaling. However, it is acknowledged that substantial contact resistance associated with the contact‐TMD interface has impeded device performance to a large extent. It has been discovered that O2 plasma treatment can convert WSe2 into WO3−x and substantially improve contact resistances of p‐type WSe2 devices by strong doping induced thinner depletion width. In this paper, temperature dependence of this conversion is studied, demonstrating an oxidation process with a precise monolayer control at room temperature and multilayer conversion at elevated temperatures. Furthermore, lateral oxidation of WSe2 underneath contact revealed by high‐resolution scanning transmission electron microscope leads to potential unpinning of the metal Fermi level and Schottky barrier lowering, resulting in lower contact resistances. The p‐doping effect is attributed to the high electron affinity of the WO3−x layer on top of the remaining WSe2 channel, and the doping level is dependent on the WO3−x thickness that is controlled by the temperature. Comprehensive materials and electrical characterizations are presented, with a low contact resistance of ≈528 Ω μm and record high on‐state current of 320 μA μm−1 at −1 V bias being reported. Tunable p‐doping on WSe2 is investigated through O2‐plasma treatment at different temperatures, with atomic control of oxidation layer characterized by transmission electron microscope. Ultralow contact resistance ≈0.5 (kΩ µm) is attributed to thinner depletion width and potential Fermi level depinning from WO3−x penetration underneath contacts, leading to record high on‐state current of 320 (µA µm−1) at VDS = −1 V.