Tunable Schottky contacts in Nb₂CO₂/HfSeS heterostructures via strain engineering and terminal functionalization

The performance of van der Waals heterostructures (vdWHs) is critically governed by their interfacial contact properties, yet achieving tunable Schottky-to-ohmic transitions remains challenging. Here, based on density functional theory, this work systematically investigates the interfacial properties and two regulation mechanisms of Nb₂CO₂/HfSeS vdWHs. By constructing different stacking configurations, the most stable structures of Nb₂CO₂/SeHfS and Nb₂CO₂/SHfSe both exhibit p-type Schottky contacts with low Schottky barrier heights (SBHs) of 0.15 eV and 0.11 eV, respectively, indicating efficient hole injection. The regulatory roles of external biaxial strain in the contact type and SBH are further elucidated. Within a strain range of -4% to +8%, the contact properties evolve significantly: under sufficient tensile strain (exceeding 6%), the contact transitions to n-type Schottky behavior, whereas under compressive strain, Nb₂CO₂/SeHfS forms an ideal ohmic contact at -2%, the other is quasi-ohmic at -2% and becomes ohmic only at -4%. This strain-induced transformation originates from strain-tuned band alignment and interfacial charge redistribution between Nb₂CO₂ and HfSeS. In addition, by modifying the functional groups of MXenes, the calculated pinning factors are 0.59 and 0.61 for the heterostructures, showing that the Schottky barrier is tunable. This work provides a theoretical foundation for accurately tuning interfacial contacts in Nb₂CO₂/semiconductor vdWHs via strain engineering and MXene terminal functionalization, offering potential implications for the exploration of high-performance strain-tunable electronic devices.