Heteroepitaxy of corundum-structured alpha-Ga2O3 thin films on alpha-Al2O3 substrates by ultrasonic mist chemical vapor deposition

Ga2O3 thin films of the alpha-phase, that is, the corundum structure (in the trigonal system), have been epitaxially obtained on sapphire (alpha-Al2O3) substrates, in contrast to the strong tendency of Ga2O3 to assume a heterogeneous crystal structure, that is, the beta-gallia structure (in the monoclinic system) on sapphire. This result is advantageous for high-quality films and is due to the growth by mist chemical vapor deposition (CVD) at low temperatures of 430-470 degrees C. The alpha-Ga2O3 films have narrow full-widths at half maximum (FWHMs) in their X-ray diffraction rocking curves, for example, about 60 arcsec. The root mean square (RMS) roughness of the surface was as small as 1 nm. The optical band gap energy obtained was 5.3eV. and the films were almost completely transparent in the near-ultraviolet and visible regions. The epitaxial growth of alpha-Ga2O3 films on sapphire is beneficial for the fabrication of oxide optical and electronic devices.