Near Field Optical Spectroscopy of Confined Excitons

Two novel approaches for mapping the microscopic carrier dynamics in semiconductor nanostructures in real space and time are discussed. Combining quasi two-color femtosecond pump–probe spectroscopy and near-field microscopy, the temporal evolution of the nonlinear change in reflectivity of a single GaAs quantum wire is imaged with a time resolution of 200 fs and a spatial resolution of 200 nm. The experiments evidence the ultrafast relaxation of carriers into a quantum wire at room temperature and carrier transport along the wire axis. The second approach is based on an optical marker technique using a novel electronically coupled wire–dot sample grown on (311)A GaAs substrates. First low temperature near-field spectra reveal the interesting properties of this nanostructure.