Synthesis and optimization of β-Ga2O3 thin films via spin-coating process

Gallium oxide (β-Ga2O3) is an ultra-wide bandgap semiconductor with a bandgap of 4.7–5.0 eV. It exhibits a high breakdown field strength and excellent thermal and chemical stability, making it promising for high-power and optoelectronic applications. Controlling substrate-dependent crystallization in solution-processed β-Ga2O3 thin films is critical for achieving high structural quality and improved optical properties. In this work, we demonstrate the synthesis of β-Ga2O3 thin films on sapphire and silicon substrates via a sol-gel spin-coating method. We systematically investigate substrate-dependent crystallization behavior through the optimization of spin-coating parameters and annealing conditions over a wide temperature range (600–1100 °C). The influence of annealing temperature on the structural, morphological, and optical properties is examined in detail. X-ray diffraction confirms the formation of the β-Ga2O3 phase above ∼800 °C. Atomic force microscopy reveals a continuous film morphology with roughness evolution attributed to initial densification followed by grain growth. UV–visible spectroscopy demonstrates a bandgap increase from ∼4.5 to 5.2 eV with increasing annealing temperature. Energy-dispersive x-ray analysis qualitatively confirms the presence of Ga and O in the films. These results provide fundamental insight into substrate-controlled crystallization in solution-processed β-Ga2O3 thin films. The optimized films may also serve as precursor layers for catalyst-free β-Ga2O3 nanostructure growth via CVD and exhibit a wide bandgap (∼5.2 eV), highlighting their potential for solar-blind UV photodetector applications.