Effect of thermal annealing on the optical and structural properties of γ-Al2O3 films prepared on MgO substrates by MOCVD

Metalorganic chemical vapor deposition (MOCVD) of gamma-Al2O3 films is performed on MgO (110) and (111) substrates by using trimethylaluminum and 02 as the precursors. The effects of post-deposition annealing on the microstructure and epitaxial relationship of the films are investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Schematic diagrams are proposed to illuminate the epitaxial relationships between the gamma-Al2O3 films and MgO substrates. The gamma-Al2O3 films annealed at 1000 degrees C exhibit the best crystalline quality, for which clear epitaxial relationships of gamma-Al2O3 (110)parallel to Mgo (110) with gamma-Al2O3 [(1) over bar 10]parallel to MgO [(1) over bar 10] and gamma-Al2O3 (111)parallel to MgO (111) with gamma-Al2O3[1 (1) over bar0]parallel to MgO [1 (1) over bar0] have been ascertained. The average transmittance of the obtained samples in the visible range is over 85%. The optical band gaps of the gamma-Al2O3 films annealed at 1000 degrees C on MgO (110) and (111) substrates are about 5.81 and 5.80 eV, respectively, which are a bit smaller than those of the as-deposited films. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.