The intensity of Eu-related luminescence from ion-implanted GaN with a 10nm thick AlN cap, both grown epitaxially by metal organic chemical vapor deposition (MOCVD) is increased markedly by high-temperature annealing at 1300°C. Photoluminescence (PL) and PL excitation (PLE) studies reveal a variety of Eu centers with different excitation mechanisms. High-resolution PL spectra at low temperature clearly show that emission lines ascribed to D05-F27 (∼622nm), D05-F37 (∼664nm), and D05-F17 (∼602nm) transitions each consist of several peaks. PL excitation spectra of the spectrally resolved components of the D05-F27 multiplet contain contributions from above-bandedge absorption by the GaN host, a GaN exciton absorption at 356nm, and a broad subedge absorption band centred at ∼385nm. Marked differences in the shape of the D05-F27 PL multiplet are demonstrated by selective excitation via the continuum/exciton states and the below gap absorption band. The four strongest lines of the multiplet are shown to consist of two pairs due to different Eu3+ centers with different excitation mechanisms.

Photoluminescence (PL) of Eu-implanted GaN epilayers grown by Metalorganic Vapour Phase Epitaxy (MOVPE) was studied as a function of temperature. The implantation was done at ion energies of 75 keV, 200 keV and 350 keV with doses of 10(14) CM-2 and 10(15) CM-2. PL spectra of all samples show the emission 5 7 31 line assigned to the D-5(0)-F-7(2) transition of EU3+ in GaN to be split into three spectral components at 620.7 nm, 621.6 nm and 622.5 nm. The split lines are seen to have very different temperature dependences of integrated intensity. Such splitting might be explained by EU3+ ion site multiplicity. The variation of the temperature quenching factor of the PL integrated intensity from sample to sample and from line to line suggests that optically active Eu3+ ions are coupled to defects and impurities, thus forming complexes with different energy position of the carrier trapping level in the bandgap of GaN. The appearance and quenching of an additional PL line at 617.3 nm with increasing temperature is observed in the range of 13-295 K

Investigation of the depth profiles and luminescence of Eu and Er-ions implanted into AlInN/GaN bilayers differentiates between ions located in the two different III-N hosts. Differences between samples implanted using channeling or off-axis geometries are studied using time-of-flight secondary ion mass spectometry. A fraction of ions have crossed the AlInN layer (either 130 or 250 nm thick) and reached the underlying GaN. Cathodoluminescence spectra as a function of incident electron energy and photoluminescence excitation data distinguish between ions within AlInN and GaN. The RE emission from the AlInN is broader and red-shifted and the dependence of the intensity on host is discussed.

This presentation reviews recent lattice location studies of rare earth (RE) ions in GaN by electron emission channelling (EC) and X-ray absorption fine structure (XAFS) techniques. These studies agree that RE ions at low concentrations (whether they are incorporated during growth or introduced later by ion implantation) predominantly occupy Ga substitutional sites, as expected from considerations of charge equivalence. We combine this result with some examples of the well-documented richness of optical spectra of GaN:RE 3+ to suggest that the luminescence of these materials may be ascribed to a family of rather similar sites, all of which feature the RE Ga defect.

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