Structural and optical properties of Al-Tb/SiO_2 multilayers fabricated by electron beam evaporation

摘要

Light emitting Al-Tb/SiO_2 nanomultilayers (NMLs) for optoelectronic applications have been produced and characterized. The active layers were deposited by electron beam evaporation onto crystalline silicon substrates, by alternatively evaporating nanometric layers of Al, Tb, and SiO_2. After deposition, all samples were submitted to an annealing treatment for 1 h in N_2 atmosphere at different temperatures, ranging from 700 to 1100℃. Transmission electron microscopy confirmed the NML structure quality, and by complementing the measurements with electron energy-loss spectroscopy, the chemical composition of the multilayers was determined at the nanoscopic level. The average composition was also measured by X-ray photoelectron spectroscopy (XPS), revealing that samples containing Al are highly oxidized. Photoluminescence experiments exhibit narrow emission lines ascribed to Tb~(3+) ions in all samples (both as-deposited and annealed ones), together with a broadband related to SiO_2 defects. The Tb-related emission intensity in the sample annealed at 1100℃ is more than one order of magnitude higher than identical samples without Al. These effects have been ascribed to the higher matrix quality, less SiO_2 defects emitting, and a better Tb~(3+) configuration in the SiO_2 matrix thanks to the higher oxygen content favored by the incorporation of Al atoms, as revealed by XPS experiments.