Substrate effects on phase formation and interfacial stability in superconducting vanadium silicide thin films

Thin films of vanadium silicide (V-silicide) in the A15 cubic phase (V3Si) are promising for superconducting quantum devices due to their high transition temperature and potential compatibility with scalable semiconductor fabrication. However, solid-phase synthesis often yields secondary silicide phases that degrade performance. Here, we investigate the influence of substrate properties using two silicon-on-insulator architectures: one with a polycrystalline HfO2 buried layer (group A) and the other with amorphous SiO2 (group B). Both systems exhibit superconductivity consistent with V3Si formation, yet structural analysis reveals mixed-phase films in both cases. Crucially, only group A maintains an atomically sharp and chemically stable interface, a prerequisite for phase purity. Prolonged annealing in group A reduces the unwanted V5Si3 phase but also leads to the emergence of Si-rich VSi2, likely due to localized substrate degradation. Preliminary atomic-resolution imaging suggests that HfO2 crystallinity may promote local phase-selective nucleation. These findings highlight the importance of substrate design in promoting phase control and maintaining interfacial integrity in superconducting silicides.