1. Institute of Novel Semiconductors State Key laboratory of Crystal Material Shandong University Jinan 250100 P. R. China
2. Shandong Crystal GaN Semiconductor Jinan 250000 P. R. China
3. Key Laboratory of Processing and Testing Technology of Glass & Functional Ceramics of Shandong, Province, School of Materials Science and Engineering Qilu University of Technology (Shandong Academy of Sciences) Jinan 250353 P. R. China
4. Shandong Research Institute of Industrial Technology Jinan 250000 P. R. China