Polarization, microscopic origin, and mode structure of luminescence and lasing from single ZnO nanowires.

The emission spectrum of individual single crystalline ZnO nanowires shows three regimes characterized by distinct polarization properties and spatial emission patterns along the length of the wire. In the visible range below 2.9 eV, emission is polarized along the long axis of the wire, along the c-axis (E//c). In the second regime between 2.9 and 3.22 eV, Fabry-Pérot guided modes polarized perpendicular to the wire (E perpendicularc) prevail. From their dispersion, it is clear that these modes signify strong coupling between the B-exciton and linearly polarized transverse electric modes that are guided by the wire and trapped between the wire end facets. The third regime is characterized by uniform emission along the wire and a marked dip in the polarization at around the electronic band gap at 3.3 eV. Lasing is observed only in the second regime in which strong light-matter interaction prevails.