Structure analysis of ELO‐GaN using a 2 × 4 μm2 micro‐beam X‐ray of an 8‐GeV storage ring

Abstract

AbstractWe investigated the micrometer‐scale structure of epitaxially laterally overgrown GaN (ELO‐GaN) using a 2 × 4 μm2 micro‐beam X‐ray of an 8‐GeV storage ring. The GaN (0 0 0 12) rocking curve of the wing region had a sharp peak with a FWHM of 46 arcsec, but that of the seed region had several broad peaks. This peak‐narrowing corresponds to the reduction of the threading dislocation (TD) density and to the increase of grain size. The grain in the wing region was typically 5 μm × 5 μm and extended along the ELO stripe of GaN 〈100〉. On the other hand, a larger grain with a 10 μm × 10 μm was observed in the wing region of another ELO‐GaN sample which did not coalesce during the growth. We conclude that the homogeneity of the GaN c‐surface tilting can be declined by coalescence of the wing regions. We believe that this inhomogeneity of the GaN c‐surface tilting and the grain size strongly affect the performance of GaN‐based laser diodes grown on ELO‐GaN. Moreover, GaN c‐surface tilting of 81.5 arcsec was observed in the wing region of ELO‐GaN although no SiO2 mask was used. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)