Lukas Wittenbecher, Emil Viñas Boström, Jan Vogelsang, Sebastian Lehman, Kimberly A. Dick, Claudio Verdozzi, Donatas Zigmantas, and Anders Mikkelsen
Hot electron relaxation and transport in nanostructures involve a multitude of ultrafast processes whose interplay and relative importance are still not fully understood, but which are relevant for future applications in areas such as photo-catalysis and optoelectronics. To unravel these processes, their dynamics in both time and space must be studied with high spatiotemporal resolution in structurally well-defined nanoscale objects. We employ time-resolved photoemission electron microscopy to image the relaxation of photogenerated hot electrons within InAs nanowires on a femtosecond time scale. We observe transport of hot electrons to the nanowire surface within 100 fs caused by surface band bending. We find that electron-hole scattering substantially influences hot electron cooling during the first few picoseconds, while phonon scattering is prominent at longer time scales. The time scale of cooling is found to differ between the well-defined wurtzite and zincblende crystal segments of the nanowires depending on excitation light polarization. The scattering and transport mechanisms identified will play a role in the rational design of nanostructures for hot electron-based applications.