1. College of Environmental Science and EngineeringBeijing Forestry University Beijing 100083 China
2. Key Laboratory of Semiconductor Materials ScienceBeijing Key Laboratory of Low Dimensional Semiconductor Materials and DevicesInstitute of SemiconductorsChinese Academy of Sciences Beijing 100083 China
3. Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100049 China
4. School of Mathematical Science and EngineeringHebei University of Engineering Handan 056038 China