1. Shaanxi Normal UniversityCollege of Physics and Information Technology Xi'an Shaanxi 710119 P. R. China
2. Xi'an University of Posts and TelecommunicationsElectronic Engineering Institute Xi'an Shaanxi 710121 P. R. China
3. Shenzhen Key Laboratory of Two-Dimensional Materials and Devices/Shenzhen Engineering Laboratory of Phosphorene and OptoelectronicsCollaborative Innovation Center for Optoelectronic Science and Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province Shenzhen 518060 Guangdong P. R. China