  In the prospect of understanding the photoluminescence mechanisms of AlN
films doped with erbium and targeting photonic applications we have synthesized
non doped and Er-doped AlN films with different crystallized nanostructures by
using PVD magnetron sputtering. Their crystalline morphology and their visible
photoluminescence properties were precisely measured.Due to the weak
cross-section absorption of rare earths like erbium, it is necessary to obtain
an efficient energy transfer mechanism between the host matrix and the rare
earth to obtain high luminescence efficiency. Our strategy is then to elaborate
some nanostructures that could introduce additional intermediate electronic
levels within the gap thanks to the presence of structural defects (point
defects, grain boundaries{\ldots}) and could lead to energy transfer from the
AlN matrix to the rare earth.Doped and non-doped AlN films were prepared by
radio frequency magnetron sputtering by using different experimental conditions
that will be detailed. It will notably be shown how a negative polarization of
samples during deposition allows obtaining crystalline morphologies ranging
from the classical columnar structure to a highly disordered polycrystalline
structure with grains of several nanometers (nearly amorphous). The
nanostructures of the films could be categorized in three types: 1) type 1 was
nanocolumnar (width of column ~ 15 nm), 2) type 2 was made of short columns
(width of column ~ 10 nm) and 3) the last type was made of equiaxed
nanocrystallites (size of grains ~3-4 nm).High-resolution photoluminescence
spectroscopy was performed to characterize their optical behaviour. The samples
were excited by the laser wavelengths at 458, 488 or 514 nm. A broad
photoluminescence band was observed centred around 520 nm in columnar samples.
In the same energy range, the highly resolved spectra also showed several sharp
emission peaks. This fine structure could be attributed to erbium transitions.
This fine structure tended to disappear going from type 1 to type 3 samples.
Indeed, the relative intensity of the peaks decreased and their full width at
half maximum increased. This change could be related to the density of defects
that increased when the size of the grains decreased. The photoluminescence
properties of the films in the visible range will be discussed in relation with
their structure.
