Excited states of neutral and charged excitons in single strongly asymmetric InP-based nanostructures emitting in the telecom C band

We investigate strongly asymmetric self-assembled nanostructures with one of the dimensions reaching hundreds of nanometers. Close to the nanowirelike type of confinement, such objects are sometimes assigned as one dimensional in nature. Here, we directly observe the spectrum of exciton excited states corresponding to longitudinal quantization. This is based on probing the optical transitions via polarization-resolved microphoto-luminescence excitation (mu PLE) measurements performed on single nanostructures combined with theoretical calculations of the neutral and charged exciton optical properties. We successfully probe absorptionlike spectra for individual bright states forming the exciton ground-state fine structure, as well as for the negatively charged exciton. Confronting the calculated spectrum of excitonic absorption with mu PLE traces, we identify optical transitions involving states that contain carriers at various excited levels related to the longest dimension. Based on a cross-polarized excitation-detection scheme, we show a very well-conserved spin configuration during orbital relaxation of the exciton from a number of excited states comparable to the quasiresonant pumping via the optical phonon, and no polarization memory for the trion, as theoretically expected.