1. Center for GaN Characterization and Analysis, Synchrotron X-Ray Characterization Group, Research Network and Facility Services Division, National Institute for Materials Science (NIMS), Kouto, Sayo, Hyogo 679-5148, Japan
2. Synchrotron X-Ray Station at Spring-8, Research Network and Facility Services Division, NIMS, Kouto, Sayo, Hyogo 679-5148, Japan
3. Synchrotron X-Ray Group, Research Center for Advanced Measurement and Characterization, NIMS, Kouto, Sayo, Hyogo 679-5148, Japan