Thermal activation, cathodo- and photoluminescence measurements of rare earth doped (Tm, Tb, Dy, Eu, Sm, Yb) amorphous/nanocrystalline AlN thin films prepared by reactive rf-sputtering

We present comprehensive cathodo- and photoluminescence measurements from thin amorphous/nanocrystalline (a/nc-) AlN films doped with rare earths. The (a/nc-) AlN films were prepared by reactive rf-sputtering using a high purity (5 N) aluminium disk in high purity nitrogen atmosphere (5 N, pressure ca. 1.3 mbar). The rare earth doping (Tm, Tb, Dy, Eu, Sm, Yb, concentrations were below 1%) was performed by placing respective rare earth metal pieces of appropriate size onto the aluminium disk. The rare earth ion emissions cover the blue (Tm), green (Tb), yellow (Dy), red (Sm, Eu) and infrared (Yb). The optical and related structural properties of the films are correlated by means of high resolution transmission electron microscopy in combination with cathodoluminescence measurements in a scanning electron microscope. In addition, the corresponding compositions are determined by energy-dispersive X-ray analysis. The cathodo- and photoluminescence spectra of the rare earth 3+ ions are recorded in the visible at 300 K in the as-grown condition (Tm, Tb, Dy, Sm, Eu, Yb) and after annealing treatments in the temperature range from 300 to 1100 °C by steps of 150 °C (Tb, Sm, Eu, Yb). The anneal-related changes in the cathodo- and photoluminescence emission spectra and in the microstructure of the films are addressed. The AlN films show nanocrystalline structure almost independent of the annealing treatment. Optimal annealing temperature for emissions of Sm and Eu doped (a/nc-) AlN were derived to be 900 °C whereas Tb3+ and Yb3+ emissions increase at least up to 1100 °C.