Effect of thermal annealing treatments on the optical properties of rare-earth-doped AlN films

Aluminium-nitrogen (AlN) films doped with samarium, europium or ytterbium have been prepared by conventional radio frequency sputtering. Because of the deposition method and conditions the as-deposited films are amorphous with Sm, Eu or Yb concentrations at low 0.5 at%. After deposition the films were submitted to cumulative isochronal thermal annealing (TA) treatments and investigated by optical transmission spectroscopy, photo- (PL) and cathodoluminescence (CL) measurements. For comparison purposes one undoped AlN film was also prepared and investigated in detail. The experimental results indicate that (a) all samples exhibit PL and CL at room temperature, (b) the main spectral features present in the AlN samples are due to defect-related transitions (undoped film) or the rare-earth (RE) ions, (c) in both cases (undoped and Sm-, Eu- or Yb-doped films) the luminescence intensity scales with the temperature of TA and (d) for the present AlN samples, there is a clear relationship between their luminescence intensity and respective energy of optical bandgaps. Finally, the effect of TA on the excitation-recombination mechanisms involving the RE ions is presented and discussed.