High-reflectivity AlN/GaN distributed Bragg reflectors grown on sapphire substrates by MOCVD

Abstract

High-reflectivity AlN/GaN distributed Bragg reflectors (DBRs) were grown on c-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD). A low temperature (LT) predeposition AlN layer and indium doping during the growth of the λ/4 AlN layers were adopted to improve the quality of the DBR. During the growth of the DBR, the structural alternation occurred abruptly when an AlN layer was grown on a GaN layer but gradually in reverse order, which resulted in a stack of quasi-three-layer periodic arrangement rather than two-layer arrangement for one growth period. The peak reflectivity of DBRs reaches 99% at the designed wavelength. The root mean square (RMS) roughness of the surface is around 4 nm over a 10 µm × 10 µm surface area of the DBR. Meanwhile, the high-reflectivity (93%) and crack-free DBR with only 16-period AlN/GaN structures was obtained by employing an optimized AlN predeposition layer.