Influence of post-deposition annealing in air and vacuum on the properties of thermally evaporated gallium oxide films

Oxidative annealing in air or reductive annealing in vacuum around 773 K of thermally evaporated gallium oxide films produces monoclinic beta-Ga2O3 films of distinctly different compositional, optical, morphological and electrical properties. The pristine films prepared by the evaporation of Ga2O3 powders are oxygen deficient, amorphous and absorbing in UV-visible region. The air annealed films are transparent (band gap similar to 4.9 eV), display nanometric granular morphology and are characterized by <1.0 eV extrinsic and 1.2-1.6 eV intrinsic activation energies in the Arrhenius plots of electrical conductivity. The growth of Ga2O3 phase on vacuum annealing takes place through the decomposition of Ga2O, one of the constituents of the pristine films. The vacuum annealed films exhibit comparatively lower transparency (band gap <4.5 eV), comprise micron-sized dendrites or fibres and have <1.0 eV extrinsic and 1.7-2.0 eV intrinsic activation energies. The incorporation of these properties results from compositional changes in films induced by annealing in air or vacuum ambient. (C) 2014 Elsevier Ltd. All rights reserved.