Oxygen Plasma Interface Engineering of Ti/n-GeSn Contacts for Ultra-Low Contact Resistivity

Abstract

Germanium-tin (GeSn) semiconductors are promising channel materials for low-power electronics owing to their high carrier mobility and compatibility with CMOS technology. However, strong Fermi-level pinning at metal/n-type GeSn interfaces causes large contact resistance, limiting device scalability and performance. Here we demonstrate an oxygen plasma interface engineering strategy that substantially reduces this contact resistance. Oxygen plasma treatment creates a self-limiting GeSnO interfacial layer that reacts with deposited Ti to form an ultrathin TiOx interlayer with favorable band alignment. The engineered TiOx interlayer is designed to reduce the effective interfacial tunneling barrier, while the slight phosphorus segregation near the contact further enhances surface doping and narrows the barrier width. Together, these synergistic effects yield an ultra-low specific contact resistivity of 2.2 × 10−7 Ω·cm2. Our scalable and CMOS-compatible approach establishes a practical route to low-resistance contacts for high-performance GeSn electronics.