报告题目：A novel picosecond time-resolved cathodoluminescence: Study of exciton dynamics in quantum wellGaN and GaN/AlGaN structures
摘要：The increasing demand for new optoelectronics devices like solar cells, laser diodes, high brightness light emitting diodes combined with the economical necessity to reach lower consumption levels and higher yields are leading researchers to develop new materials. More particularly a lot of investments are being made to better understand fundamental opto-electronic properties of compound semiconductor material at nanoscale, including studies of quantum wells, quantum dots, or nanowire structures. Conventionally used optical technique, such as fluorescence microscopy, provides a spatial resolution that remains limited to a fraction of a micrometer. More advanced near-field optical microscopy, can be used to gain spectroscopic information at the 100-nanometre scale, but acquisition of luminescence emission, especially transient signals, presents a challenge.
In this seminar we will talk about novel picosecond time-resolved cathodoluminescence system with demonstrated combined time resolution of <12 ps, and spatial resolution of <50 nm. Application of the system for characterization of excitonic dynamics of quantum wells in non-polar GaN and GaN/AlGaN material will be presented. We first study exciton localization and recombination processes in a-plane GaN and show that they are strongly dependent on the local basal stacking fault (BSF) density. The change in BSF-bound exciton luminescence decay time is explained through direct relation to the local BSF density. As a next step we proceeded to grow an (Al, Ga)N/GaN single QW by molecular beam epitaxy on the studied GaN sample. We then study local relaxation-recombination dynamics of excitons in both QW and QWRs formed at the intersection between BSFs and QWs. We explain the large range of values reported so far for the exciton radiative lifetimes in non-polar (Al,Ga)N/GaN QWs.
报告人：Olivier Gougeon and Samuel Sonderegger(Attolight AG, Lausanne Switzerland)
报告时间：11月5号上午9：00
报告地点：学术沙龙室
欢迎感兴趣的各位老师和学生参加!