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Quantization effects on optical polarization switching in ð11 " 22Þ-oriented InGaN/GaN quantum-well (QW) structures, which were not evident in the previous report by Ueda et al., have been firmly confirmed. The present study found that polarization ratios became more negative as the luminescence photon energy was decreased from 2.6 eV. Enhancement in optical polarization was found in thin QW structures, which is believed to be a result of quantization effects. Sample structures containing thick InGaN and AlGaN layers showed polarization ratios shifted towards positive values; these samples exhibited in-plane luminescence inhomogeneity with stripe morphologies parallel to ½1 " 100 and dark lines appearing at angles between 50 and 62 with respect to ½1 " 100. #

Semipolar (1122) plane III–nitride laser diodes (LDs) were realized on low extended defect density semipolar (1122) GaN bulk substrates. The LD structures were grown by conventional atmospheric-pressure metal organic chemical vapor deposition (MOCVD), using conditions similar to that of c-plane nitride device growth. The mirror facet for a laser cavity was formed by dry-etching of III–V nitride films without cleaving. Stimulated emission was observed at 426.9 nm with a full width at half maximum (FWHM) of less than 1 nm. The (1122) plane laser diode had threshold currents (Ith) of 306 mA, corresponding to a threshold current densities (Jth) of 12.8 kA/cm2.

Optical and electrical characteristics of InGaN/GaN quantum-well (QW) light-emitting diodes (LEDs) are the subjects of this study. Samples were prepared on nonpolar (1 0   0) and semipolar (1 1   2) orientations of bulk GaN substrates. Electrical-bias-applied photoluminescence was employed as a characterization technique. It was confirmed that saturation of reverse photocurrent occurred around 0 V in nonpolar LEDs and at positive voltages in (1 1   2)-oriented LEDs, while our previous study found negative voltages in (0 0 0 1)-oriented LEDs (Masui et al 2008 J. Phys. D: Appl. Phys. 41 165105). These results indicated that (1 1   2)-oriented InGaN/GaN QWs experience piezoelectric fields being in the same direction as the built-in field. Piezoelectric field intensity was estimated to be −0.3 MV cm−1 in the (1 1   2)-oriented QW structure. Spectral comparison between photoluminescence and electroluminescence of the LED samples exhibited a tendency that spectral differences were insignificant in single-QW LEDs.