Role of self-formed InGaN quantum dots for exciton localization in the purple laser diode emitting at 420 nm

Structural analysis was performed on a purple laser diode composed of $In0.20$$Ga0.80$N (3 nm)/ $In0.05$$Ga0.95$N (6 nm) multiple quantum wells, by employing transmission electron microscopy and energy-dispersive x-ray microanalysis, both of which are assessed from the cross-sectional direction. It was found that the contrast of light and shade in the well layers corresponds to the difference in In composition. The main radiative recombination was attributed to excitons localized at deep traps which probably originate from the In-rich region in the wells acting as quantum dots. Photopumped lasing was observed at the high energy side of the main spontaneous emission bands.