GaN-based vertical cavity lasers with semiconductor/dielectric and all dielectric reflectors

摘要

GaN-based vertical cavity structures containing bottom AlN/GaN DBRs with top dielectric DBRs on freestanding c-GaN and all dielectric DBRs on GaN on c-sapphire were investigated. Epitaxial lateral overgrowth (ELO) technique allowed the use of both top and bottom all dielectric reflector stacks without substrate removal and the fabrication of the active region containing InGaN multiple quantum wells entirely on the nearly defect-free laterally grown wing regions to avoid nonradiative centers caused by extended and point defects. Compared with the cavity containing hybrid-DBRs on freestanding GaN, the cavity with all dielectric DBRs exhibited quality factors up to 1200 at high optical excitation and an order of magnitude lower stimulated emission threshold density (nearly 5 μJ/cm~2). Vertical to lateral growth ratio for ELO could be enhanced up to 5 by increasing the Ⅴ-Ⅲ ratio and employment of NH_3 modulation, which minimizes the use of dry etching to reduce the cavity thickness and therefore is promising for high quality vertical cavities with all dielectric DBRs.