We report on the impact of compressive strain on (100)-oriented $\beta \text{−}\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ epitaxial thin films grown on partially strain-relaxed monoclinic $\theta \text{−}\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$ buffer layers by oxygen-radical-assisted pulsed-laser deposition. Reflection high-energy electron diffraction was used to monitor the in-plane lattice spacing during the deposition. This observation revealed that the tensile strain in the $\theta \text{−}\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$ buffer layer on the (100) $\beta \text{−}\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ substrate gradually relaxed by the formation of misfit dislocations, whereas the $\beta \text{−}\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ epilayer adapted the lattice spacing of the $\theta \text{−}\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$ buffer layer up to −3% lattice mismatch along the $b$-axis direction. The widening of the band gap of $\beta \text{−}\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ with increasing compressive strain was observed from both reflection electron energy-loss spectroscopy and polarized optical reflectance measurements. Experimental results are supported by results from density functional theory calculations.

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• Epitaxial strain
• Wide band gap systems
• Density functional theory