Controlling Schottky to Ohmic Transition at the 2D GaAs/Ge Heterojunction via Surface Adsorption-Driven Substrate Tailoring

For electronic nanodevices, achieving low contact resistance depends critically on the Ohmic contact at the metal–semiconductor (M–S) interface. This contact enhances device performance by systematically lowering the Schottky barrier height (SBH) and reducing the interface state density. Although standard methods such as applying mechanical strain or adjusting the vertical electric field can reliably produce Ohmic contact, they consistently damage the M–S interface, which eventually compromises device dependability. In response to this issue, we propose a strategy called surface adsorption-driven substrate tailoring (SADST), which operates without involving the M–S interface and simultaneously preserves its structural integrity. Our results show that by optimizing the adsorption sites and coverage of cesium on GaAs surfaces (Cs@GaAs), the interfacial electronic structure of two-dimensional (2D) GaAs/Ge van der Waals heterostructures (vdWHs) can be effectively reshaped. Consequently, a substantial drop in SBH occurs, which enables a dependable shift from Schottky to Ohmic behavior. To break this down further, when Cs is adsorbed onto GaAs, the work function ( ϕ ) decreases, electron injection becomes more efficient, interfacial carrier tunneling probability ( P TB ) rises, and Fermi level pinning (FLP) gets fully eliminated. Moreover, analyzing both the transmission coefficient and current–voltage ( I – V ) curves verifies that Cs adsorption is crucial for creating an efficient Ohmic contact. Employing Cs as a nondamaging, interface-decoupled tuning agent opens up a viable pathway for fabricating GaAs-based electronic nanodevices that possess superior contact properties.