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 ͑PL͒ and PL excitation ͑PLE͒ spectra of Eu-implanted Al x Ga 1−x N are obtained across the whole alloy composition range. The dominant 5 D 0 -7 F 2 emission band broadens and then narrows as x increases from 0 to 1 while the peak shifts monotonically. This behavior is surprisingly similar to the broadening of excitons in a semiconductor alloy caused by composition fluctuations ͓E. F. Schubert et al., Phys. Rev. B 30, 813 ͑1984͔͒. PLE spectra reveal a steplike Al x Ga 1−x N band-edge absorption and two "subgap" bands X 1,2 :X 1 peaks at 3.26 eV in GaN and shifts linearly to 3.54 eV in AlN. For x Ͼ 0.6, X 2 emerges approximately 1 eV higher in energy than X 1 and shifts in a similar way. We propose that X 1,2 involve creation of coreexcitonic complexes of Eu emitting centers.

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We have studied the structural and optical properties of In x Al 1−x N alloys with compositions nearly lattice-matched to GaN. Scanning electron microscopy measurements reveals a good overall surface quality, with some defect structures distributed across the surface whose density increases with the InN concentration. On the other hand, Raman scattering experiments show three peaks in the frequency range between 500 and 900 cm −1 , which have been assigned to InN-like and AlN-like E 2 modes and A 1 (LO) mode of the In x Al 1−x N. These results agree with theoretical calculations previously reported where two-mode and one-mode behavior was predicted for the E 2 and A 1 (LO) modes, respectively. Photoluminescence and photoluminescence excitation allowed us to determine the emission and absorption energies of the In x Al 1−x N epilayers. Both energies display a redshift as the InN fraction increases. We find a roughly linear increase of the Stokes shift with InN fraction, with Stokes shift values of ≈ 0.5 eV in the composition range close to the lattice-matched condition.

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.