Current injection to free-standing III-N nanowires by bipolar diffusion

Light-emitting diodes (LEDs) based on nanowires are expected to enable a superior alternative to conventional LEDs due to their higher light extraction efficiency, reduced droop, and reduced material consumption. However, efficient current injection to nanowires with conventional current spreading approaches is challenging, because the conventional approach requires doping the wires and using at least partly absorbing top contacts. We show that minority carrier diffusion provides an extremely interesting possibility for current injection to undoped free-standing nanowires that do not require top contacts. To investigate this possibility, we have simulated current transport in selected nanowire structures where the nanowires are located close to a separate pn homojunction. Our results suggest that with bipolar diffusion injection, injection efficiencies exceeding 80% are feasible even for unoptimized free-standing nanowire structures at current densities up to 100 A/cm ², with a maximum injection efficiency of approximately 95% at 0.1 A/cm². The results suggest that the concept also extends to other near surface nanostructures such as quantum wells coupled to surface plasmons and, under reverse operation, to photovoltaic devices.