Growth Temperature Dependence of Heteroepitaxial (Al,Ga) 2 O 3 Thin Films on c‐Plane Sapphire Substrates

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(Al,Ga) 2 O 3 thin filmswere deposited on c‐plane sapphire substrates by mist chemical vapor deposition at 600–900 °C using nominal Al/Ga precursor molar ratios of 0.10, 0.20, and 0.30. β ‐related diffraction, out‐of‐plane orientation distribution, surface roughness, local film thickness, and optical absorption were systematically compared within this 4 × 3 process matrix. β ‐related reflections were detected for all precursor ratios at 700 and 800 °C, whereas their detectability depended on the precursor ratio at 600 °C. No distinct film‐related diffraction peaks were resolved at 900 °C. Although 800 °C produced the lowest surface roughness under all precursor conditions, the corresponding rocking‐curve full widths at half maximum (FWHMs) were broader than those at 700 °C, demonstrating that surface smoothing did not coincide with improved out‐of‐plane alignment. The locally measured film thicknesses ranged from approximately 238–619 nm. The apparent local growth rates generally decreased with increasing growth temperature, whereas their dependence on the nominal Al/Ga precursor ratio was less systematic. The apparent optical transition energies ranged from 4.80 to 5.34 eV and varied nonmonotonically with growth temperature and nominal precursor ratio.