Influence of patterned TiO₂/SiO₂ dielectric multilayers for back and front mirror facetson GaN-based laser diodes

Ridge InGaN multi-quantum-well-structure (MQW) edge-emitting laser diodes (LDs) were grown on (0001) sapphire substrates by low-pressure metal-organic chemical vapour deposition (MOCVD). The dielectric TiO_2/SiO_2 front and back facet coatings as cavity mirror facets of the LDs have been deposited with electron-beam evaporation method. The reflectivity of the designed front coating is about 50% and that of the back high reflective coating is as high as 99.9%. Under pulsed current injection at room temperature, the influences of the dielectric facets were discussed. The threshold current of the ridge GaN-based LDs was decreased after the deposition of the back high reflective dielectric mirrors and decreased again after the front facets were deposited. Above the threshold, the slope efficiency of the LDs with both reflective facets was larger than those with only back facets and without any reflective facets. It is important to design the reflectivity of the front facets for improving the performance of GaN-based LDs.