Unraveling the Ultrafast Hot Electron Dynamics in Semiconductor Nanowires.

Lukas Wittenbecher,Kimberly A Dick,Claudio Verdozzi,Anders Mikkelsen,Donatas Zigmantas,Sebastian Lehman,Jan Vogelsang,Emil Viñas Boström

doi:10.1021/acsnano.0c08101

Abstract

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 photocatalysis 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.

Highlights

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 photocatalysis and optoelectronics
Studies using Tr-PEEM have focused on investigating plasmonic near fields in metallic nanoparticles and nanostructured films.[41−43] More recently, the technique has been applied to the study of charge carrier dynamics at semiconductor surfaces and interfaces.[44−49]
A scanning electron microscopy (SEM) image of a typical NW is presented in Figure 1b, showing the axial stacking of Wz and Zb segments and the gold seed particle atop the NW

Summary

Introduction

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 photocatalysis and optoelectronics. The evolution of the hot carrier distribution in space and energy is important for their efficient extraction and usage,[8,9] and an understanding of this evolution is crucial for guiding the design of future hot-carrier-based devices For such devices, the use of nanomaterials is highly favorable as they allow for a strong concentration of hot carriers[10,11] and can be engineered to reduce carrier−phonon scattering rates, extending hot carrier lifetimes.[12,13] This has sparked intense research on ultrafast hot carrier dynamics in various materials, such as plasmonic nanoparticles,[14] III−V semiconductor materials,[15] and lead-halide perovskites.[16,17] III−V semiconductor nanowires (NWs), in particular, allow for the combination of several functional materials into a single nanostructure, enabling the creation of tailored energy filters for hot electron extraction.[18,19] This, in combination with the high degree of control over the NW growth process, makes these nanostructures a promising platform for hot-carrierbased semiconductor devices and for exploring the fundamental processes governing carrier transport and relaxation.

Methods

Results

Conclusion