Optical spectroscopy study of carriers recombination in quantum wires

We report the optical properties of high quality V-groove GaAs/Al0.3Ga0.7.As quantum wires (QWRs) with different thicknesses of the GaAs layer. The systematic investigation of photoluminescence (PL) and photoluminescence excitation (PLE) spectra as a function of the wire size combined with model calculations allows us to study in detail the effect of two-dimensional quantum confinement on valence band mixing and polarization anisotropy. We show that the polarization anisotropy of PL spectra critically depends on localization effects thus making any polarization analysis based on extended states insufficient at low temperature. The influence of exciton localization and surface corrugation on PLE spectra is also clarified; the observed large polarization anisotropy is unambiguously related to the one-dimensional (1D) character of our QWRs. Comparison of the experimental results obtained for all three QWR samples with theoretical predictions is clearly compatible with a strong suppression of the 1D band-edge singularity in PLE spectra. The temperature dependence of PL and PLE spectra for QWRs of different thicknesses is investigated. We are able to measure photoluminescence up to room temperature due to high quantum efficiency. Additionally, large subband spacings and small inhomogeneous broadenings allow us to perform PLE measurements up to high temperature (100 – 200 K, depending on the wire size). A thermally-enhanced transfer of carriers from the side-QWs into the QWRs is evidenced and attributed to increasing 2D exciton mobilities with increasing temperature and to the combination of classical activation and tunneling through the potential barrier due to the "necking" in the side quantum Wells (QWs) next to the QWRs. A strong impact of disorder on the PL (PLE) peak position and on the line shape is clearly shown. The evolution of the PL and PLE peak positions with increasing temperature together with a line shape analysis of PL spectra indicates the dominance of excitonic effects over the whole temperature range. The enhancement of the lowest-energy PLE peak with respect to higher-energy transitions with increasing temperature is explained in terms of an effective mobility edge. The variation of the full width at half maximum of PL and PLE spectra with increasing temperature is attributed to the combined effects of structural disorder and exciton-phonon scattering. We measure PL spectra of our high-quality QWRs through holes which vary from 2.0 μm clown to 0.2 μm in width (micro-PL experiments). For sufficiently thin QWRs it is possible to observe directly the localization of 1D excitons in local potential minima. PL spectra detected through the smallest apertures (0.2 μm) are attributed to recombination of excitons in isolated quantum dot (QD)-like potentials wells. Homogeneously broadened lines can be resolved. The correlation between structural disorder and micro-PL features is studied. We determine the most realistic wire morphology as infe