Ultrafast carrier dynamics in a single quantum wire studied by near-field pump and probe spectroscopy

Summary form only given. Far-field femtosecond spectroscopic studies provide direct insight into the dephasing, scattering and energy relaxation of free carrier and excitons in semiconductors. In general, however, such studies give less direct information on the ballistic and diffusive real-space transfer of photogenerated carriers or their trapping into low-dimensional nanostructures, processes that involve the real-space motion of carriers on length scales of 10-1000 nm, beyond the spatial resolution of far-field spectroscopy. The combination of femtosecond spectroscopy with microscopy techniques giving subwavelength resolution offers new perspectives for a direct investigation of such processes. We combine near-field microscopy and two-color femtosecond pump and probe spectroscopy to investigate the carrier dynamics in a GaAs single quantum wire (QWR) structure with a spatial resolution of 200 nm and a temporal resolution of 200 fs. We give evidence for the ultrafast relaxation of carriers in a single QWR and for quasi-one-dimensional carrier transport on a ps time and 100 nm length scale at room temperature.