Characterization of strain effects on structure, surface morphology, and band gap of MOVPE grown β-Ga2O3 thin films on β-(AlxGa1-x)2O3 substrates

β-Ga ₂ O ₃ thin films (~ 83 nm) were grown on β-(AlₓGa _1-x ) ₂ O₃ (x = 0.1, 0.15, 0.2) (100) substrates via metal-organic vapor phase epitaxy (MOVPE) and characterized by high resolution x-ray diffraction (HR-XRD), atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). HR-XRD confirmed the coherent epitaxial growth of β-Ga ₂ O ₃ thin films, with the strain state exhibiting a direct dependence on the aluminum composition (x) in the substrate. AFM showed a surface roughness of about 0.3 nm which is not affected by the incorporated epitaxial strain. T hickness dependence of b-Ga ₂ O ₃ grown on β-(AlₓGa _1-x ) ₂ O₃ (x = 0.2) was investigated, revealing that the film remained fully strained up to a thickness of 247 nm and maintained smooth surfaces. Band gap energies for films (83 nm) grown under compressive lattice strain were determined by spectroscopic ellipsometry in a large energy range between 1.5–6.5 eV using the Tauc-Lorentz dispersion model. While the band gap of the substrate increases linearly with increasing Al content, a slight enhancement in the band gap of the film was observed with increasing Al content up to x = 0.15, beyond which no further change was detected at x = 0.2. These results suggest that the MOVPE technique is promising for producing β-Ga ₂ O ₃ with controlled band gap and developing heterojunction devices.