1. School of Electronic Information and Engineering Xi'an Technological University Xi'an 710021 P. R. China
2. Shaanxi Key Laboratory of Photoelectric Functional Materials and Devices Xi'an Technological University Xi'an 710021 P. R. China
3. School of Mechanical Engineering Northwestern Polytechnical University Xi'an 710072 P. R. China
4. Institute of Electronics and Systems University of Montpellier Montpellier 34095 France