  We present the combined analysis of the electroluminescence (EL) as well as
the current-voltage (I-V) behavior of single, freestanding (In,Ga)N/GaN
nanowire (NW) light-emitting diodes (LEDs) in an unprocessed, self-assembled
ensemble grown by molecular beam epitaxy. The data were acquired in a scanning
electron microscope equipped with a micromanipulator and a luminescence
detection system. Single NW spectra consist of emission lines originating from
different quantum wells, and the width of the spectra increases with decreasing
peak emission energy. The corresponding I-V characteristics are described well
by the modified Shockley equation. The key advantage of this measurement
approach is the possibility to correlate the EL intensity of a single NW LED
with the actual current density in this NW. This way, the external quantum
efficiency (EQE) can be investigated as a function of the current in a single
NW LED. The comparison of the EQE characteristic of single NWs and the ensemble
device allows a quite accurate determination of the actual number of emitting
NWs in the working ensemble LED and the respective current densities in its
individual NWs. This information is decisive for a meaningful and comprehensive
characterization of a NW ensemble device, rendering the measurement approach
employed here a very powerful analysis tool.
