Tunable Fermi Level Alignment in TMD Contacts via Semimetallic Bi-Sb Alloys.

Atomically thin two-dimensional semiconductors, such as transition metal dichalcogenides (TMDs), are ushering in a new era beyond silicon-based technology. However, the persistent Fermi level pinning (FLP) effect, caused by metal-induced gap states (MIGS), creates an undesired Schottky barrier at the metal-semiconductor interface, leading to high contact resistance and degraded device performance. To broaden the applicability of TMD materials, it is crucial to establish a simple method to tune and align the Fermi levels (E F) of contact metals with those of TMDs, particularly as TMD-based devices continue to develop. Herein, we propose a strategy that uses semimetal alloys, such as bismuth-antimony (Bi-Sb), to modify the E F of contact metals. These alloys not only eliminate MIGS-related contact issues but also enable tunable E F tailored to different TMD materials. Our results reveal that the performance of MoS2 and WS2 field-effect transistors strongly correlates with the E F of their contact alloys, which vary with the Bi-Sb alloy composition. The optimized device configuration exhibits a Schottky-barrier-free interface with minimal contact resistance, resulting from E F alignment between the contact metal and the semiconductor. For MoS2 devices, Bi0.03Sb0.97 achieves a contact resistance of 530 Ω·μm, and a mobility of 50 cm2/V·s. Beyond mitigating the effects of MIGS and FLP, this work introduces a novel approach to energy level alignment, thereby broadening the scope of applications for 2D materials.