  Er-doped aluminum nitride films, containing different Er concentrations, were
obtained at room temperature by reactive radio frequency magnetron sputtering.
The prepared samples show a nano-columnar microstructure and the size of the
columns is dependent on the magnetron power. The Er-related photoluminescence
(PL) was studied in relation with the temperature, the Er content and the
microstructure. Steady-state PL, PL excitation spectroscopy and time-resolved
PL were performed. Both visible and near infrared PL were obtained at room
temperature for the as-deposited samples. It is demonstrated that the PL
intensity reaches a maximum for an Er concentration equal to 1 at. % and that
the PL efficiency is an increasing function of the magnetron power. Decay time
measurements show the important role of defect related non radiative
recombination, assumed to be correlated to the presence of grain boundaries.
Moreover PL excitation results demonstrate that an indirect excitation of Er 3+
ions occurs for excitation wavelengths lower than 600 nm. It is also suggested
that Er ions occupy at least two different sites in the AlN host matrix.
