MOCVD growth of β-phase (Al_xGa_(1-x))_2O_3 on (201) β-Ga_2O_3 substrates

摘要

β-(Al_xGa_(1-x))_2O_3 thin films are grown on (201) β-Ga_2O_3 substrates via metal organic chemical vapor deposition to investigate the solubility of Al in β-phase Ga_2O_3. The x-ray diffraction (XRD) spectra reveal crystalline quality (201) β-(Al_xGa_(1-x))_2O_3 thin films with Al compositions up to 48%. The Al compositions are further confirmed by high resolution x-ray spectroscopy measurements and energy-dispersive x-ray spectra (EDS) mapping. The bandgap energies extracted from XPS spectra range between 5.20 ± 0.06 eV and 5.72 ± 0.08 eV for x = 21%-48%. The surface morphology evaluated by both scanning electron microscopy and atomic force microscopy shows elongated features with granules along the [010] direction, which are suppressed with the increasing Al content. A systematic growth study through tuning growth parameters indicates that the chamber pressure plays an important role in both surface morphology and Al incorporation. Material characterization via high resolution scanning transmission electron microscopy and STEM-EDS reveals Al fluctuations in the sample with the 48% Al composition. Atomic resolution STEM imaging and XRD spectra for (201) β-(Al_xGa_(1-x))_2O_3/Ga_2O_3 superlattice structures confirm that the periodicity of the β-(Al_xGa_(1-x))_2O_3/Ga_2O_3 sub-layers is well maintained with high-Al compositions.