GaN-based blue laser diodes

We report our recent progress on GaN-based high-power laser diodes (LDs), w hich will be applied as a light source in high-density optical storage syst ems. We have developed raised-pressure metal-organic chemical vapour deposi tion (R-P-MOCVD), which can reduce the threading-dislocation density in the GaN layer to several times 10(8) cm(-2), and demonstrated continuous-wave (cw) operation of GaN-based LD grown by RP-MOCVD. Furthermore, we found tha t the epitaxial lateral overgrowth (ELO) technique is useful for further re ducing threading-dislocation density to 10(6) cm(-2) and reducing the rough ness of the cleaved facet. By using this growth technique and optimizing de vice parameters, the lifetime of LDs was improved to more than 1000 hours u nder 30 mW cw operation at 60 degreesC. Our results proved that reducing bo th threading-dislocation density and consumption power is a valid approach to realizing a practical GaN-based LD. On the other hand, the practical GaN -based LD was obtained when threading-dislocation density in ELO-GaN was on ly reduced to 10(6) cm(-2), which is a relatively small reduction as compar ed with threading-dislocation density in GaAs- and InP-based LDs. We believ e that the multiplication of non-radiative centres is very slow in GaN-base d LDs, possibly due to the innate character of the GaN-based semiconductor itself.