arXiv subjects

Ziying Xiang

Publications and source records attributed to Ziying Xiang.

2 recordsLinked to original sources

arXiv2025

Unified interface dipole theory for Fermi level pinning effect at metal-semiconductor contacts

We present a unified bond dipole theory for metal-semiconductor interfaces to explain the microscopic origin of interface dipoles and Fermi level pinning (FLP) in terms of Harrison's bond-orbital model. By combining first-principles calculations with tight-binding analysis, we show that localized bonding between semiconductor surface dangling bonds and metal orbitals is sufficient to generate a large interface dipole and induce strong FLP, even when only a single metal monolayer is present. Within this framework, metal-induced gap states (MIGS), dangling-bond-induced surface states (DBSS), and bonding states embedded in the valence band are all understood as different outcomes of the same underlying interface bonding mechanism, rather than as independent causes of FLP. We further establish that the key parameter governing FLP strength is the density of surface dangling bonds that can form new chemical bonds with the metal, which directly controls the magnitude of the bond-induced interface dipole. This picture naturally explains the weaker pinning observed in more ionic semiconductors than in covalent ones and provides practical guidance for engineering metal-semiconductor interfaces and tuning Schottky barrier heights.

cond-mat.mtrl-sci↗

arXiv2025

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 Femi level pinning (FLP) in the metal-semiconductors contacts. Here, we unravel unambiguously that the dangling bonds-induced interface states play a crucial role, even comparable with MIGS. The first-principles calculations show that metal-Ge and metal-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 substantially 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 new light on alleviating the Femi level pinning to lower the contact resistance for Si and emerging materials towards advanced semiconductor technology.

cond-mat.mtrl-sci↗