Ultrafast electron dynamics in ZnO/Si micro-cones

A comparative study of the ultrafast dynamics on ZnO thin films deposited on flat Si substrates and on Si micro-cones following ultrashort laser excitation has been carried out using time-resolved optical spectroscopy. By monitoring the transient band gap renormalization induced by nonlinearly excited carriers it is found that fast electron scattering and trapping occurs more efficiently in the micro-cones as compared to the flat films. This enhanced trapping efficiency is attributed to the defects and imperfections that are introduced by the increased surface roughness due to the conical shape.