Strain relief mechanisms and growth behavior of superlattice distributed Bragg reflectors

Abstract

AbstractIn this work, the successful use of AlN/GaN superlattices (SL) as the low‐index λ/4 layer of distributed Bragg reflectors (DBR) is demonstrated. DBR samples were grown with MOVPE on 2 inch sapphire substrates and a standard GaN buffer structure. The samples were characterized using high‐resolution X‐ray diffraction (HRXRD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and white‐light reflectometry. With this concept, effective Al contents of 30% in the low‐index layers of the DBR can be realized without the occurrence of layer cracking or relaxation. This is attributed to a staircase propagation of the TD in the DBR structure. By kinking into the in‐plane direction, the TD is able to relieve in‐plane strain on a micro‐scale. In this way, relaxation or cracking of the whole layer can be prohibited. A study of growth rate optimization was performed. As a result, the growth rate of the DBR was increased maintaining the high interface quality and optical performance. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)