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

The metal-induced gap states (MIGS) are commonly believed to cause the strong Fermi level pinning (FLP) in the metal-semiconductor contacts. Here, we reveal that the dangling-bond-induced surface states play a crucial role, even comparable with MIGS. The first-principles calculations show that metal-germanium (Ge) and metal-silicon (Si) contacts should possess a similar FLP strength if they adopt an identical interface bonding configuration: the reconstructed bonding configuration renders Si and Ge having pinning factors of 0.16 and 0.11, respectively, and the ideal non-reconstructed bonding configuration gives them pinning factors of 0.05 and 0, respectively. We illustrate that Si favors the reconstructed bonding configuration, and Ge favors the ideal non-reconstructed bonding configuration after metal deposition. The self-passivation of the dangling bonds reduces the interface gap states to give a much weaker FLP in the metal-Si contacts than in the metal-Ge contacts. We also demonstrate that the full passivation of the interface dangling bonds can further increase the pinning factor to 0.5 by further reducing the interface gap states. These findings shed light on alleviating the FLP to lower the contact resistance for Si and emerging materials towards advanced semiconductor technology.