Phase engineering of κ-Ga2O3 heteroepitaxy on LiNbO3 by strain competition effect

Phase engineering through strain modulation has emerged as an effective strategy for tailoring the properties of polymorphic oxide semiconductors. This study demonstrates the heteroepitaxial growth of orthorhombic κ-Ga2O3 on LiNbO3, focusing on phase engineering via strain competition between thermal expansion and lattice mismatch. By varying the growth temperature from 510 to 590 °C, the in-plane strain in κ-Ga2O3 was tuned from tensile (+0.16%) to compressive (−0.17%). High-resolution x-ray diffraction and transmission electron microscopy revealed that elevated temperatures induce compressive strain, suppressing the formation of a thick γ-Ga2O3 transition layer and enabling atomically sharp interfaces between the κ- and γ-Ga2O3. This strain engineering significantly improves film crystallinity, reduces domain twisting disorder, and improves interfacial quality. Atomic-scale analyses via high-angle annular dark-field scanning transmission electron microscopy confirmed the stacking sequences (A–B–A*–B*) and the out-of-plane inversion symmetry breaking along κ-Ga2O3 [001], establishing the structural origin of its ferroelectric polarization and laying the groundwork for polarization engineering in future ferroelectric device applications.