Growth, structure, and superconducting transport in atomically thin near-single-crystal aluminum films on GaAs(111)A

2D superconductivity occurs in ultra-thin superconductors, where enhanced quantum fluctuations and disorder significantly affect their superconducting properties. In this work, a  few-monolayer Al films were studied to explore superconductivity near the 2D limit.

Ultra-thin Al films grown on GaAs(111)A were structurally characterized using in-situ RHEED and ex-situ synchrotron-radiation(SR) XRD. RHEED patterns exhibited streaky features, indicating the formation of highly ordered Al(111) layers. SR-XRD radial scans revealed broad Al(111) diffraction peaks overlapping with the adjacent GaAs(111) substrate tail. Crystal truncation rod simulations based on few-monolayer-thick Al films successfully reproduced the observed Al(111) peak positions and widths. Azimuthal φ-scans across off-normal Al{111̅} reflections revealed peaks separated by 120°, indicating the single-domain feature.

Superconducting fluctuation effects, preserved by in-situ Al₂O₃ passivation, were investigated via ex-situ transport measurements. Superconducting transition curves were analyzed using Aslamazov-Larkin and Maki-Thompson fluctuation models, revealing insights into dimensional disorder mechanisms. The critical temperature (T_c)​ and pair-breaking parameter (δ) were extracted from the fits, showing enhanced scattering in thinner films.