Near-single-domain superconducting aluminium films on GaAs(111)A with remarkable crystalline quality for scalable quantum circuits

The realization of highly coherent and scalable superconducting quantum circuits relies critically on the structural perfection of epitaxial aluminium (Al) films. However, the presence of twin boundaries in these materials introduces prominent decoherence channels that severely limit device performance. Here, we have reproducibly grown near-single-domain superconducting Al films on GaAs(111)A wafers using molecular beam epitaxy. Synchrotron X-ray diffraction revealed twin-domain ratios of 0.00005 and 0.0003 for 19.4-nm- and 9.6-nm-thick films, respectively—the lowest reported for Al on any substrate and long considered unattainable for practical device platforms. Azimuthal scans across off-normal Al{111̄} reflections exhibit narrow full width at half maximum (FWHM) values down to 0.55°, unmatched by epi-Al grown by any other method. Normal scans showed a well-defined (111) orientation with pronounced Pendellösung fringes, and θ-rocking-curve FWHM values down to 0.018°; the former indicates abrupt film–substrate and oxide–film interfaces. Electron backscatter diffraction mapping confirms macroscopic in-plane uniformity and the absence of Σ3 twin domains. Atomic force microscopy and scanning transmission electron microscopy confirmed atomically smooth surfaces and abrupt heterointerfaces. The films exhibit critical temperatures approaching bulk values, establishing a materials platform for scalable, high-coherence superconducting qubits. The structural perfection of epitaxial aluminium films is crucial for advancing superconducting quantum circuits, yet twin boundaries hinder device performance. Here, the authors achieve near-single-domain superconducting Al films on Ga-terminated GaAs(111) wafers, demonstrating ultralow twin-domain ratios, atomically smooth surfaces, and abrupt heterointerfaces, paving the way for scalable, high-performance quantum devices.