Pump-probe Spectroscopy of Single InGaAs and InGaAs/InP Nanowires: Shedding Light on the Wurtzite Band Structure and Carrier Dynamics*

We use transient Rayleigh scattering to optically characterize the band structure and carrier dynamics of single wurtzite nanowires. We employ a 1.51 eV pump and a tunable near-infrared probe (0.79 to 1.16 eV) to study core-only InGaAs nanowires as well as strained core-shell InGaAs-InP heterostructures at 300 K and 10 K. We observe an electronic transition in low temperature core-only spectra at 0.86 eV, a higher energy than the fundamental bandgap of bulk zincblende InGaAs of similar composition. We observe a corresponding transition in core-shell spectra at 0.97 eV. The blue-shift of the transition energy for the core-shell nanowire relative to the core-only nanowire is consistent with compressive strain in the InGaAs core. We report an order of magnitude enhancement in the 10 K carrier lifetimes of the core-shell nanowires (2100 ps) compared to the core-only nanowires (90 ps). Numerical modeling of our TRS spectra provides further insight into the thermalization of charge carriers after photoexcitation.