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Total polarization charge for different AlGaInN alloy compositions in the Ga-rich composition range of Ga0.5In0.5N−Al0.5Ga0.5N−GaN. The yellow circle marks the QW composition and the red ones the barrier compositions with sample A (GaN barrier) at the top to sample D at the bottom. In principle, polarization matching is achieved, e.g. along the black line for a barrier composition around Al0.13Ga0.58In0.29N and an EG of ∼2.70 eV with a rather low band offset to the Ga0.75In0.25N QW with EG ∼ 2.46 eV.
FE-SEM images of the surfaces of samples A (a) and D (b). All samples with quaternary barrier layers show an increasing density of surface defects with increasing In and Al content.
GIID Θ-2 Θ scan of the GaN ( ) diffraction peak. Compared to a reference sample (GaN buffer) all diffraction scans show a shoulder at lower angle originating in a very weak lattice relaxation of the MQW system. The peak around 31.1° originates from the W Lα radiation (tungsten contamination of the anode).
PL spectra (full lines) and simulated data (dotted lines) of the four samples, which show a blue-shift due to a decreasing QCSE with increasing Al and In composition of the barrier layers.
Sample parameters as determined by XRD, growth, and material parameters. In-plane strain ε is given between buffer and barrier layer. The InGaN QW thickness is assumed to 2.5 nm with 25% In concentration and ε = −0.027.
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