High electron mobility in strained core/shell nanowires revealed by optical pump – THz probe spectroscopy

Optical pump – THz probe spectroscopy has been established as a tool for contactless probing of electronic transport in semiconductor nanowires (NWs) [1]. Particularly in III-V NWs, scattering rates of charge carriers, as well as their plasmonic resonances for typical doping levels, are located in the THz range. The analysis of the optical conductivity spectra using the localized surface plasmon model provides an estimation of the carrier density and the mobility.
Here, we employ THz spectroscopy to study electron mobility in the strained GaAs core of GaAs/InAlAs core/shell nanowires. Owing to the lattice mismatch between the core and the shell in these NWs, the bandgap energy in the strained GaAs core exhibits a reduction by up to 40% [2]. Our results demonstrate that this effect is accompanied by a notable increase in the electron mobility by 30-50% with respect to a bulk GaAs [3]. We discuss the role of various scattering mechanisms and their dependence on strain and temperature. In addition to the homogeneous plasmon broadening caused by the carrier scattering, we also observe an inhomogeneous broadening in dense ensembles of NWs as illustrated in Fig. 1(a). Our modelling demonstrates that such broadening stems from the plasmonic interaction between neighboring NWs leading to the shift of the plasmon frequency as shown in Fig. 1(b). This effect has to be considered in the analysis of THz response of NWs since it may result in a significant underestimation of the mobility values.