An adsorption-induced substrate engineering strategy for Ohmic contact conversion in GaAs/Ge van der Waals metal–semiconductor interface

• Cs adsorption-induced strategy independent of M−S interface maintains its stability. • Cs adsorption enables Schottky to Ohmic contact transition in GaAs/Ge vdWHs. • Interface dipole work function synergy enables intrinsic Ohmic contact mechanism. • Cs adsorption enables 57.8 % tunneling probability and high FLP suppression (S = 0.75). • I-V and tunneling spectra confirm Ohmic contact with enhanced carrier injection. Ohmic contact at the metal–semiconductor (M−S) interface plays a pivotal role in improving the performance of electronic nanodevices, by systematically reducing the Schottky barrier height (SBH) and minimizing the density of interface states, which is essential for achieving low contact resistance. Although conventional approaches involving stress application or vertical electric field modulation successfully achieve Ohmic contact, they invariably cause interfacial degradation at M−S interface, ultimately impairing device reliability. To address this challenge, we propose a novel adsorption-induced substrate engineering (AISE) strategy that functions independently of the M−S interface while maintaining its structural stability. We demonstrate that cesium adsorption on GaAs surfaces (Cs@GaAs), optimized in terms of adsorption sites and coverage, effectively reconstructs the interfacial electronic structure of two-dimensional (2D) GaAs/Ge van der Waals heterostructures (vdWHs). This leads to a substantial reduction in the SBH, enabling the stable conversion from Schottky to Ohmic contact. Specifically, Cs adsorption lowers the work function ( ϕ ) of GaAs, enhances electron injection and interfacial carrier tunneling probability ( P TB ), and successfully suppresses Fermi level pinning (FLP). Furthermore, analysis of the transmission coefficient and current–voltage (I-V) characteristics confirms the pivotal role of Cs adsorption in driving the formation of an efficient Ohmic contact. The use of Cs as a non-destructive and interface-independent modulator, offers a promising pathway for the development of GaAs-based electronic nanodevices featuring superior contact properties.