Electron mobility and lifetime in GaAs/In𝑥Ga1−𝑥As core/shell nanowires studied by optical pump – THz probe spectroscopy

We utilize ultrafast optical pump – terahertz probe spectroscopy in order to investigate charge carrier response of GaAs/In𝑥Ga1−𝑥As core/shell nanowires (NWs) produced by molecular beam epitaxy. The NWs were ≈2 𝜇m long. The GaAs core diameter was 25nm and the InGaAs shell thickness was 80 nm. We studied the shells with different compositions, from 𝑥 = 0.20 to 𝑥 = 0.44.
From the pump-probe measurements we extracted terahertz photoconductivity of NWs and used the localized surface plasmon model to fit the results. The charge carrier lifetimes were estimated to be around 80–100 ps while the extracted electron mobilities reach 3700 cm2V−1s−1 at room temperature. Even without a surface passivation shell, these values are higher than those in previously studied GaAs/AlGaAs core/shell nanowires, but still lower than the ones for bulk InGaAs. Possible reasons (sources of electron scattering) which affect the mobility will be discussed.