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Tunable Fermi Level Alignment in TMD Contacts via Semimetallic Bi-Sb Alloys
Chi-Chun Cheng1, Henry J H Chen2, Chang-Hong Shen3
1Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan.
ACS Omega
|August 14, 2026
Summary
Researchers developed a new method using bismuth-antimony (Bi-Sb) alloys to tune metal Fermi levels, overcoming Fermi level pinning (FLP) in 2D semiconductors. This approach reduces contact resistance and enhances device performance for transition metal dichalcogenides (TMDs).
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Atomically thin two-dimensional semiconductors (TMDs) offer a promising alternative to silicon-based technologies.
- Fermi level pinning (FLP) caused by metal-induced gap states (MIGS) creates Schottky barriers, increasing contact resistance and hindering device performance in TMDs.
- Effective Fermi level alignment between contact metals and TMDs is crucial for advancing 2D material-based devices.
Purpose of the Study:
- To introduce a simple and effective method for tuning the Fermi level (EF) of contact metals for 2D semiconductors.
- To investigate the use of semimetal alloys, specifically bismuth-antimony (Bi-Sb), to modify EF and mitigate MIGS-related issues.
- To demonstrate improved performance in TMD-based field-effect transistors through optimized Fermi level alignment.
Main Methods:
- Utilized bismuth-antimony (Bi-Sb) alloy compositions to tune the Fermi level (EF) of contact metals.
- Fabricated MoS2 and WS2 field-effect transistors with Bi-Sb alloy contacts.
- Characterized the metal-semiconductor interface, contact resistance, and device performance as a function of alloy composition.
Main Results:
- Bi-Sb alloys successfully eliminated MIGS-related contact issues and enabled tunable EF.
- Device performance of MoS2 and WS2 transistors showed a strong correlation with the EF of the Bi-Sb contact alloys.
- Optimized devices achieved a Schottky-barrier-free interface with significantly reduced contact resistance (e.g., 530 Ω·μm for MoS2 with Bi0.03Sb0.97) and improved mobility (50 cm2/V·s).
Conclusions:
- Bismuth-antimony alloys provide a versatile strategy for engineering Fermi level alignment in 2D semiconductor devices.
- This approach effectively mitigates Fermi level pinning and metal-induced gap states, leading to enhanced device performance.
- The findings open new avenues for utilizing 2D materials in advanced electronic applications by enabling precise control over metal-semiconductor interfaces.
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