Growth of a high-quality α-Ga2O3 thin film on a-plane sapphire by sol–gel spin coating and rapid thermal annealing

초록

α-Ga2O3 has attracted attention as a key material for next-generation power semiconductor devices and deep-ultraviolet optoelectronic devices owing to its widest energy bandgap (∼5.3 eV) and high critical electric field (∼9.5 MV/cm) among Ga2O3 polymorphs. In addition, α-Ga2O3 has a highly symmetric corundum structure, which is beneficial for oriented thin-film growth on sapphire substrates and bandgap engineering with other corundum-structured oxides. However, high-quality α-Ga2O3 thin films are typically grown by vapor-phase methods that require expensive equipment and stringent process control, limiting scalability to large-area production and mass manufacturing. In this study, high-quality α-Ga2O3 thin films with preferential (110) orientation were fabricated on a corundum-structured a-plane sapphire (110) substrate, which has a small in-plane lattice mismatch with α-Ga2O3, using a low-cost sol–gel spin coating process followed by rapid thermal annealing in an O2 atmosphere. The effects of annealing temperature on the phase formation and the surface, optical, and chemical properties of the films were investigated, and a phase-pure α-Ga2O3 film was obtained at an optimized annealing temperature of 600 °C, exhibiting a uniform surface morphology, high optical transmittance in the UV–visible region, and weak defect-related signatures in photoluminescence and X-ray photoelectron spectroscopy analyses. These results demonstrate that high-quality, (110)-preferentially oriented, pure α-Ga2O3 thin films can be realized on a-plane sapphire via simple, low-cost solution processing, providing evidence for process scalability and potential cost reduction of α-Ga2O3 thin-film technology and helping lower the barrier to commercialization of α-Ga2O3-based devices.

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