Lattice vibrations and optical properties of α-Ga₂O₃ films grown by halide vapor phase epitaxy

The lattice vibrations and optical properties of α-Ga2O3 are investigated by polarized Raman scattering and spectroscopic ellipsometry measurements at room temperature. Three types of epitaxial α-Ga2O3 film samples were grown on c-plane sapphire substrates by halide vapor phase epitaxy (HVPE) in three different growth modes, namely by O2-control, Ga-control, and reference mode. Seven Raman active phonons and three infrared active phonons are determined experimentally for all samples. The relative intensities of Eg(2), Eg(4), and Eg(5) modes in Raman spectra varies as a function of growth mode. The growth mode has no obvious effect on the infrared active Eu(2) and Eu(4) modes, while phonon lifetime of the Eu(3) mode drastically changes. For the Eu(3) mode, the O2-control sample exhibits a significantly reduced broadening factor of 7.6 cm−1 compared with that of the reference (10 cm−1), and the Ga-control (16.6 cm−1) samples. All the three types of samples show similar complex ordinary dielectric functions in the spectral range between 0.5 and 6.5 eV indicating no obvious changes within the band structure by changing the growth mode.