Annealing-induced interfacial evolution of β-Ga2O3 (001)/4H-SiC heterostructures fabricated by surface-activated bonding

β-Ga 2 O 3 /4H-SiC heterostructures are promising for the heterogeneous integration of ultrawide-bandgap semiconductors, yet the thermal evolution of their bonded interfaces remains insufficiently understood. In this work, β-Ga 2 O 3 (001) and 4H-SiC wafers were directly bonded by surface-activated bonding, and the interfacial microstructure and elemental distribution were systematically examined in the as-bonded state and after annealing at 500 and 1000 °C. Microstructural analysis revealed a continuous disordered interfacial layer with an average thickness of approximately 9.0 nm in the as-bonded sample. After annealing at 500 °C, the interfacial layer slightly decreased to approximately 8.0 nm and exhibited a more compact configuration, indicating moderate thermally induced interfacial densification and rearrangement. In contrast, annealing at 1000 °C led to pronounced interfacial reconstruction, producing a markedly thickened and spatially non-uniform transition region with an average thickness of 19.4 ± 5.5 nm. Energy-dispersive X-ray spectroscopy mapping and line-scan analyses confirmed the elemental transition across the bonded interface. Fe enrichment was consistently observed near the interface, while projected Fe intensity profiles derived from elemental maps showed a substantial broadening of the Fe distribution after annealing at 1000 °C. These results demonstrate a temperature-dependent evolution of the surface-activated bonded β-Ga 2 O 3 /4H-SiC interface, from a thin disordered interlayer in the as-bonded state to a slightly densified interface after moderate annealing and a reconstructed, non-uniform transition region after high-temperature annealing. This work provides useful guidance for the interfacial design and thermal processing of β-Ga 2 O 3 /4H-SiC heterogeneous integration.