X-ray microdiffraction imaging investigations of wing tilt in epitaxially overgrown GaN

The crystalline quality in epitaxially laterally overgrown (ELO) GaN and the amount of wing tilt is characterized on a local basis, with high spatial and angular resolution. A method of full-field X-ray microdiffraction imaging, termed rocking curve imaging, is used to record simultaneously a large set of local X-ray diffraction profiles originating from sample surface areas of micrometer size. x-omega maps of diffracted intensity allow to quantify the amount of wing tilt in individual lateral ELO periods as well as to monitor the fluctuations of tilt between adjacent periods. Automated shape analysis of the full set of local rocking curves provides a means to quantitatively characterize the local crystalline perfection of GaN. The ELO window and wing regions can be clearly separated; comparison indicates an average improvement of crystal quality by a factor 3–4 due to the lateral overgrowth process.