Single-domain, semiconducting κ-Ga2O3 grown on isostructural ε-GaFeO3 templates

The epitaxial growth of a phase-pure, single-domain, semiconducting κ-Ga2O3 thin film is demonstrated. Multiferroic ε-GaFeO3, being isostructural to κ-Ga2O3, was used as a substrate and was initially covered by a high-temperature MIST-CVD κ-Ga2O3 seed layer. Subsequently, tin-assisted pulsed laser deposition at 550 °C was applied to grow the single-crystalline epilayer with a thickness of 400 nm. The structural properties were investigated by x-ray diffraction and transmission electron microscopy. A reciprocal space map revealed that the κ-Ga2O3 layer sustains residual strain and is only partially relaxed. Consistently, misfit dislocations were observed, indicating ongoing but incomplete strain relaxation. Secondary ion mass spectrometry confirmed efficient Sn incorporation and revealed Fe diffusion from the ε-GaFeO3 substrate. The Fe impurities segregate predominantly at the advancing growth front, resulting in only moderate bulk compensation of the κ-Ga2O3/ε-GaFeO3 layer. Temperature-dependent in-plane transport measurements revealed freeze out of free electrons with activation energies of Ea,1=48 meV and Ea,2=253 meV at intermediate and high temperatures, respectively. No measurable in-plane conductivity was observed for a reference sample deposited on c-plane sapphire, which exhibited in-plane rotational domains and nanocolumnar growth. These results demonstrate that epitaxial growth on isostructural ε-GaFeO3 enables single-crystalline, semiconducting κ-Ga2O3 and establishes the κ-Ga2O3/ε-GaFeO3 heterostructure as a promising platform for exploring polarization-charge-induced two-dimensional electron gases in multifunctional ferroelectric/ferrimagnetic oxide systems.