Fundamental Understanding of Interface Chemistry and Electrical Contact Properties of Bi and MoS₂

The interface properties and thermal stability of bismuth (Bi) contacts on molybdenum disulfide (MoS₂) shed light on their behavior under various deposition conditions and temperatures. The examination involves extensive techniques including X-ray photoelectron spectroscopy, scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). Bi contacts formed a van der Waals interface on MoS₂ regardless of deposition conditions, such as ultrahigh vacuum (UHV, 3 × 10^-11 mbar) and high vacuum (HV, 4 × 10^-6 mbar), while the oxidation on MoS₂ has been observed. However, the semimetallic properties of Bi suppress the impact of defect states, including oxidized-MoS₂ and vacancies. Notably, the n-type characteristic of Bi/MoS₂ remains unaffected, and no significant changes in the local density of states near the conduction band minimum are observed despite the presence of defects detected by STM and STS. As a result, the Fermi level (E_F) resides below the conduction band of MoS₂. The study also examines the impact of annealing on the contact interface, revealing no interface reaction between Bi and MoS₂ up to 300 °C. These findings enhance our understanding of semimetal (Bi) contacts on MoS₂, with implications for improving the performance and reliability of electronic devices.