Spectroscopic characterization of phase transformation in Ge-rich Al2O3 films grown by magnetron co-sputtering

Thermally-stimulated evolution of optical and structural properties of Ge-rich-Al2O3 films with different Ge contents was investigated. As-deposited films and films annealed at T-A <= 550 degrees C were found to be amorphous whatever the Ge content. The formation of amorphous Ge clusters occurs at T-A = 550 degrees C, whereas their crystallization is prominent at T-A = 600 degrees C requiring a shorter annealing time for the higher Ge content. The films annealed at T-A = 550 degrees C showed broad photoluminescence spectrum. Its shape and intensity depend on Ge content and excitation energy. Annealing at T-A = 600 degrees C results in the appearance of additional UV bands originated from the formation of GeO x phase covered Ge clusters. An analysis of excitation spectra was performed to distinguish the mechanism of light emission in these films as well as to discriminate contribution of carrier recombination in the Ge phase (amorphous clusters and/or nanocrystals) as well as via interface or host defects. The concentration and mobility of free carriers was also estimated. (C) 2020 Elsevier B.V. All rights reserved.