Self-passivation reduces the Fermi level pinning in the metal-semiconductor contacts

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Metal-induced gap states (MIGS) are traditionally considered the primary cause of Fermi level pinning (FLP) in metal-semiconductor contacts.
• However, the role of other interface states, such as those originating from dangling bonds, remains less understood.

Purpose of the Study:

• To investigate the contribution of dangling-bond-induced surface states to Fermi level pinning in metal-germanium (Ge) and metal-silicon (Si) contacts.
• To compare the FLP strength in metal-Si and metal-Ge contacts under different interface bonding configurations.
• To explore methods for alleviating FLP by passivating interface dangling bonds.

Main Methods:

• First-principles calculations were employed to model metal-Ge and metal-Si contacts.
• Analysis of interface bonding configurations, including reconstructed and ideal non-reconstructed types.
• Quantification of pinning factors for different interface scenarios.

Main Results:

• Dangling-bond-induced surface states play a crucial role in FLP, comparable to MIGS.
• Metal-Si contacts exhibit weaker FLP than metal-Ge contacts due to the self-passivation of dangling bonds, favoring reconstructed bonding.
• Ge favors ideal non-reconstructed bonding, leading to stronger FLP.
• Full passivation of dangling bonds can significantly increase the pinning factor.

Conclusions:

• Interface dangling bonds are critical determinants of FLP strength in metal-semiconductor contacts.
• The differing bonding preferences of Si and Ge at interfaces explain their distinct FLP behaviors.
• Strategies to passivate dangling bonds offer a pathway to reduce FLP and lower contact resistance for advanced semiconductor devices.