Attainment of atomically abrupt Interfaces in Al₂O₃/Al/GaAs heterostructures with high-crystallinity single-domain Al films and in situ oxide deposition

In superconducting quantum devices, the quality of interface is critical for maintaining long coherence times. Disordered grain boundaries and interfacial inhomogeneities between superconducting thin films and adjacent layers introduce energy relaxation channels that degrade qubit performance. In this work, we achieved single-domain Al films with a low twin ratio, which along with in situ oxide deposition led to Al₂O₃/Al/GaAs heterostructures with atomically abrupt interfaces, essential for enhancing quantum coherence.

Synchrotron X-ray diffraction normal scans of the Al films exhibited clear Pendellösung fringes, indicating excellent film quality. In-plane scans revealed an extremely low twin ratio of 0.005%, surpassing previous results of Al films grown on sapphire and Si substrates. AFM and STEM confirmed smooth surfaces and ordered interfaces. X-ray reflectivity (XRR) measurements further demonstrated the exceptionally smooth interface and uniformity of the Al₂O₃/Al/GaAs heterostructures, with well-defined interference fringes, indicative of precise control over layer thicknesses. The XRR fitting revealed minimal roughness at the interfaces. These results highlight the high structural integrity of the heterostructures, crucial for reducing interface-related loss mechanisms and boosting the performance of superconducting quantum devices.