Strain-mediated compositional pulling effect in α -(AlxGa1−x)2O3 heteroepitaxy

Precise compositional control is essential for tailoring α-(AlxGa1−x)2O3 heterostructures, yet is often compromised by the compositional pulling effect (CPE) during heteroepitaxy. Here, α-(AlxGa1−x)2O3 epilayers spanning a broad Al-composition range of x = 0.42–0.92 were grown on nonpolar m-plane sapphire substrates to elucidate the strain-mediated origin of the CPE. Critical-thickness calculations, reciprocal-space mapping, energy-dispersive x-ray spectroscopy, and geometric phase analysis collectively identify a composition-dependent transition from strain-relaxed growth of α-(AlxGa1−x)2O3 at x = 0.42–0.62 to fully strained pseudomorphic growth at x = 0.71–0.92. The relaxed α-(AlxGa1−x)2O3 epilayers exhibit pronounced Al enrichment near the heterointerface, with the compositional grading length contracting from approximately 72 to 22 nm as the Al composition increases, whereas the fully strained α-(AlxGa1−x)2O3 epilayers are compositionally uniform. Comparative growth of α-(Al0.40Ga0.60)2O3 on sapphire and α-Ga2O3 templates further reveals a reversal of the cation-redistribution pathway: compressive strain promotes Al incorporation, while tensile strain drives Ga enrichment. These results establish the CPE as a bidirectional, strain-mediated cation-incorporation response and provide a physical basis for interfacial composition engineering in α-(AlxGa1−x)2O3 heterostructures.