Microstructure of a-plane (2110) GaN ELOG stripe patterns with different in-plane orientation

摘要

Nonpolar epitaxial lateral overgrown (ELOG) GaN ridges with different in-plane orientations were studied using cathodoluminescence (CL) and micro-Raman spectroscopy. The high density of threading dislocations (TD) and basal plane stacking faults (BSF) in a-plane GaN on r-plane sapphire requires a defect reduction, e.g. via ELOG, in order to realize efficient emission from light emitting diodes (LEDs) or lasers. The distribution of TDs and BSFs is derived from plan view and cross sectional spectrally resolved CL micrographs. For [0001] stripe orientations BSFs and TDs spread into the laterally overgrown material (wing). In [0111] oriented stripes TDs are mostly restricted to the region on top of the mask opening (window), whereas BSFs extend into the wing region. A reduction of BSF and TDs in the wing region was observed for [0110] oriented stripes. Cross sectional Raman mapping of an [0110] oriented GaN ridge shows reduced strain and improved crystalline quality in the wing regions.