Photoluminescence of Eu-doped GaN thin films prepared by radio frequency magnetron sputtering

The Eu-doped GaN thin films (GaN:Eu) were deposited on the sapphire substrate by means of the rf magnetron sputtering method. The GaN:Eu films were characterized by x-ray diffraction, scanning electron microscope, and photoluminescence (PL). Although as-grown GaN:Eu films (2mol% Eu in target) exhibited weak broad Eu-related red PL, the annealing in NH3 atmosphere (1000°C for 1h) led to the remarkable enhancement of Eu-related PL lines. PL spectra of such annealed GaN:Eu films exhibited a series of sharp PL lines characteristic of substitutional Eu3+ ions at Ga sites in the GaN lattice (dominant PL line is at 622nm for the D05–F27 transition). On the other hand for GaN:Eu films (5mol% Eu in target), as-grown films are amorphous and exhibited broad Eu3+-related PL lines. The annealing led to the crystallization of the films, the elimination of Eu3+-related PL lines, and the enhancement of the near-band-edge PL. The Eu-luminescent centers are considered to be removed during the crystallization.