GaN-based blue laser diodes

Abstract

We report our recent progress on GaN-based high-power laser diodes (LDs),which will be applied as a light source in high-density optical storagesystems. We have developed raised-pressure metal-organic chemical vapourdeposition (RP-MOCVD), which can reduce the threading-dislocation density inthe GaN layer to several times 108 cm-2, and demonstratedcontinuous-wave (cw) operation of GaN-based LD grown by RP-MOCVD. Furthermore,we found that the epitaxial lateral overgrowth (ELO) technique is useful forfurther reducing threading-dislocation density to 106 cm-2and reducing the roughness of the cleaved facet. By using this growthtechnique and optimizing device parameters, the lifetime of LDs was improvedto more than 1000 hours under 30 mW cw operation at 60 °C. Our resultsproved that reducing both threading-dislocation density and consumption poweris 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 inELO-GaN was only reduced to 106 cm-2, which is a relatively smallreduction as compared with threading-dislocation density in GaAs- andInP-based LDs. We believe that the multiplication of non-radiative centres isvery slow in GaN-based LDs, possibly due to the innate character of theGaN-based semiconductor itself.