Above-bandgap photoexcitation of semiconductors results in the generation of ‘hot’ electrons with considerable excess energy. Studying properties and dynamics of these photogenerated hot carriers provides insights into elementary scattering mechanisms in solids on the ultrafast time scale and might eventually lead to efficient hot-electron based devices in photodetection, catalysis or solar energy conversion.
We use time-resolved photoemission electron microscopy (TR-PEEM) to follow the relaxation of photogenerated hot electrons in III-V semiconductor nanowires. Using the sub-50nm spatial resolution of the PEEM, we can resolve separate segments of nanowire heterostructures and investigate the correlation between local structure and relaxation dynamics.
In our recent work on InAs nanowires , we focused on hot electron dynamics within the first few ps after excitation. We found that hot electrons are transported to the nanowire surface on a 100 fs time scale due to surface band bending, and experimental evidence suggests that significant cooling occurs within the first ps via electron-hole scattering. Nanowire segments of the same material but different crystal phase (wurtzite or zinc-blende) were found to exhibit different cooling dynamics which could be attributed to the different optical properties of wurtzite/zinc blende InAs.
 Wittenbecher, L.; Viñas Boström, E.; Vogelsang, J.; Lehman, S.; Dick, K. A.; Verdozzi, C.; Zigmantas, D.; Mikkelsen, A. Unraveling the Ultrafast Hot Electron Dynamics in Semiconductor Nanowires. ACS Nano 2021. doi.org/10.1021/acsnano.0c08101.