Temperature Dependent Exciton Funnel Dynamics in Uniform Strain Gradient Field Observed by Time-Resolved Photoluminescence

Elastic strain engineering is an important way to reversibly tune the properties of micro/nanoscale semiconductors for promising applications in the emerging advanced nanotechnologies, such as the strain enhanced high-mobility transistors, nanogenerators, etc. However, direct observation and control of energetic carrier dynamics with precise strain gradient fields remains a challenge. Here, observation of temperature-dependent exciton funnel dynamics is reported in a precisely controlled strain gradient field by time-resolved photoluminescence. An efficient exciton hopping process is revealed at picosecond time scale as the donor-bound excitons in ZnO microwires funnel along the strain gradient, which strongly depends on the temperature. Combined experiments and simulations unravel that, in addition to the exciton funnel by the strain gradient, both the excitation efficiency and emission lifetime of the excitons increase gradually from the compressive side to the tensile side due to the role of local strain regulation. The results give a clear physical picture of the energetic carrier dynamics in the strain gradient field in semiconductors, which provides a promising paradigm for the design of high-performance optoelectronic devices.