Optimizing the electronic structures and carrier dynamics in semiconductors at atomic scale is an essential issue for innovative device applications and improving their functions, especially important for the micro/nano-scale optoelectronic devices.The previous investigations of Prof. Dapeng Yu in School of Physics have demonstrated that, due to the much higher elastic strain in micro/nano-scale materials than their bulk counterpart (Physical Review B 73, 235409, 2006), the stain effect of semiconductors would be magnified at micro/nano-scale (Advanced Materials 21, 4937, 2009), and the strain gradient may play an important role in micro/nano-scale semiconductors (Advanced Materials 24，4707，2012). Therefore, elastic strainhas been proposed as a possible knob to tailor the electronic structure and carrier dynamics in semiconductors.Recently, major progresses have been achieved on elastic strain engineered semiconductor micro/nano-structures.However, how does the elastic inhomogeneous strain field influence the carrier dynamics in semiconductors is still elusive and a big challenge due to the difficulty in precisely creating and controlling an elastic inhomogeneous strain field in micro/nano-structures and the lack of an powerful experimental characterization technique with enough spatial and temporal resolutions.

Most recently, the Ph.D student Xuewen Fu and associate Prof. Zhimin Liao etc. in Prof. Dapeng Yu’s group, which is affiliated with the National State Key Laboratory of ‘Artificial Microstructure and MesoscopicPhysics’, and Collaborative Innovation Centerof Quantum Material Science, have achieved great progresses in tailoring exciton and carrier dynamics of semiconductors via elastic strain gradient. They designed the experiment elaborately and realized the standard 4-point-bending test on ZnOmico/nanowires for the first, then throughthe careful continue-wave cathodoluminescence (CW-CL) measurements on the purely bent ZnO micro/nanowires at low temperature (5.5 K), an abnormal over-all redshift of up to 60 meV was observed at the whole pure bending cross. They carried out collaboration with Prof. Ji Feng in the International Center of Quantum Materialsat Peking University, Prof. Ju Li at MIT and Prof. WanlinGuo at Nanjing University of Aeronautics and Astronautics, based on the theoretic analysis and model numerical simulation, they proposedthat the abnormal experimental phenomenon above is due to the elastic strain gradient driving effect on theexcitons. These results werepublishedon one of the top journals in the field of Nanomaterials and Nanoscience: Advanced Materials (Advanced Materials 2014, 26, 2572, Xuewen Fu, et al.) on January 27.

After that, in order to confirm and observe theexciton drift effect under elastic strain gradient by experiment directly, Mr. Xuewen Fu has been sent to EPFL in Switzerland for half a year and carried collaboration with Prof. Benoit Deveaud’s group. By using the unique time resolved cathodoluminescence (TRCL) setup with both high spatial and temporal resolutions in EPFL, they further carried out investigation on the picosecond resolved exciton dynamics of purely bent ZnO micro/nanowires and directly observed the elastic strain gradient driving effect on the excitons, demonstrating the important role of strain gradient effect in semiconductors, i.e. the strain gradient can be effectively used to tunetheexciton and carrier dynamics in semiconductors. It has great guiding significance forthedevelopment of new kind semiconductor optoelectronic devices. These results were published on another top journal in the field of Nanomaterials and Nanoscience: ACS Nano (ACS Nano 2014, 8 (4), 3412. Xuewen Fu, et al.)onMarch21. This work is a significant breakthrough in the area of semiconductor exciton and carrier dynamics via high spatial and temporal resolution investigation, and is alsothe unique report in this field in China. Prof. Ji Feng in the International Center of Quantum Materials at Peking University and Prof. WanlinGuo at Nanjing University of Aeronautics and Astronautics, have done great theoretic contributions to this work.

This work was supported by National Natural Science Foundation, China/Swiss Cooperation Project, National 973 Program, National State Key Laboratory of ‘Artificial Microstructure and Mesoscopic Physics’, and Collaborative Innovation Center of Quantum Material Science.