GaN-Based Vertical Cavities with All Dielectric Reflectors by Epitaxial Lateral Overgrowth

GaN-based vertical cavities with all dielectric top and bottom distributed Bragg reflectors (DBRs) on c-plane sapphire were investigated under optical injection and compared with those having AlN/GaN bottom and dielectric top DBRs on freestanding GaN. A novel fabrication method employing two epitaxial lateral overgrowth steps is introduced to produce a cavity on bottom dielectric DBRs without the need to remove the sapphire substrate. Under high optical excitation, the cavity with all dielectric DBRs exhibited quality factors up to 1400 and an order of magnitude lower stimulated emission threshold density (5 µJ/cm2) than those employing top dielectric DBRs but semiconductor AlN/GaN bottom DBRs on freestanding GaN. This novel approach is expected to lead to injection vertical cavity lasers with naturally formed nearly defect-free active regions and current confinement without any oxidation steps.