Growth and characterization of highly reflective AlInN/AlGaN Bragg reflectors

We report on the growth of distributed Bragg reflectors (DBRs) with up to 40 periods based on lattice matched Al0.85In0.15N/Al0.2Ga0.8N layers. Using an Al0.2Ga0.8N buffer, which is directly grown on the c-plane sapphire substrate, stress relief through crack formation or by relaxation processes can be prevented, which is confirmed by Nomarski microscopy and X-ray reciprocal space maps. The structures exhibit homogenous layer thicknesses and sharp interfaces, as revealed by FE-SEM images, in-situ reflectivity measurements and high resolution X-ray diffraction. These properties allow the growth of DBRs with reflectivities higher than 99 % at a wavelength of ∼360 nm. Such mirrors are very promising for the use in high Q-factor microcavities for the subsequent realization of GaN-based VCSELs or the observation of strong exciton-photon coupling.