Cathodoluminescence studies of chevron features in semi-polar (11-22) InGaN/GaN multiple quantum well structures

Epitaxial overgrowth of semi-polar III-nitride layers and devices often leads to arrowhead-shaped surface features, referred to as chevrons. We report on a study into the optical, structural and electrical properties of these features occurring in two very different semi-polar structures, a blue-emitting multiple quantum well (MQW) structure and an amber-emitting light-emitting diode (LED). Cathodoluminescence (CL) hyperspectral imaging has highlighted shifts in their emission energy, occurring in the region of the chevron. These variations are due to different semi-polar planes introduced in the chevron arms resulting in a lack of uniformity in the InN incorporation across samples, and the disruption of the structure which could cause a narrowing of the QWs in this region. Atomic force microscopy has revealed that chevrons can penetrate over 150 nm into the sample, and quench light emission from the active layers. The dominance of non-radiative recombination in the chevron region was exposed by simultaneous measurement of CL and the electron beam-induced current (EBIC). Overall these results provide an overview of the nature and impact of chevrons on the luminescence of semi-polar devices.