Transmission electron microscopical investigation of AlGaN/GaN distributed Bragg reflectors

AlGaN/GaN distributed Bragg reflectors (DBRs) with 40 mirror pairs were investigated by transmission electron microscopy. The structures were analysed for defects, interfaces, layer thicknesses and composition in order to reveal possible reasons for the experimentally obtained reflectivity falling behind the theoretically expected one. A low crack density and a homogeneous Al‐concentration in the AlGaN‐layers was found. Nevertheless, the threading dislocation density was significant, and numerous inversion domains were observed, which originate in the AlGaN‐buffer layer below the DBR‐structure. In addition, the thickness of the GaN‐DBR layers measured along the growth direction of the DBR exhibits large variations, and the interfaces are broad with extensions of ∼ 10% of the intended layer thickness (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)