Group IV semiconductors, silicon, germanium, and carbon are today's most important cubic diamond structure forming semiconductors. A recently developed rhombohedral super-hetero epitaxy technology has enabled the single-crystal growth of cubic diamond semiconductors on the basal plane of selected trigonal crystals. This kind of hetero-crystal-structure epitaxy was previously thought to be impossible or very difficult to grow. We found this apparent lacuna in the earlier studies to be stemming from the lack of a proper characterization tool and a deficit in the knowledge of growth parameters employed. Here, we present X-ray diffraction (XRD) methods for characterizing twin crystal defects in the rhombohedral-trigonal epitaxy scheme. These XRD methods not only measure the total density of the twin defect crystals but also map their distribution on the wafer with high sensitivity and spatial resolution.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.