  Light emitting diodes (LEDs) were fabricated using ensembles of free-standing
(In,Ga)N/GaN nanowires (NWs) grown on Si substrates in the self-induced growth
mode by molecular beam epitaxy. Electron beam induced current analysis,
cathodoluminescence as well as biased $\mu$-photoluminescence spectroscopy,
transmission electron microscopy, and electrical measurements indicate that the
electroluminescence of such LEDs is governed by the differences in the
individual current densities of the single-NW LEDs operated in parallel, i.e.
by the inhomogeneity of the current path in the ensemble LED. In addition, the
optoelectronic characterization leads to the conclusion that these NWs exhibit
N-polarity and that the (In,Ga)N quantum well states in the NWs are subject to
a non-vanishing quantum confined Stark effect.
