Electroluminescence and current-voltage measurements of single (In,Ga)N/GaN nanowire light-emitting diodes in the nanowire ensemble

TL;DR

This study combines electroluminescence and I-V measurements of individual (In,Ga)N/GaN nanowire LEDs within an ensemble, enabling detailed analysis of efficiency and current distribution at the single-wire level.

Contribution

It introduces a novel measurement approach that correlates single nanowire electroluminescence with current density, improving ensemble LED characterization.

Findings

Single nanowire spectra show multiple emission lines from different quantum wells.

The I-V characteristics fit the modified Shockley equation well.

The method allows accurate determination of the number of active nanowires and their current densities.

Abstract

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.