Nonradiative recombination mechanism in phosphor-free gan-based nanowire white light emitting diodes and the effect of ammonium sulfide surface Passivation

We report on a detailed investigation of nonradiative recombination processes in InGaN/GaN dot-in-a-wire white light emitting diodes (LEDs) grown by molecular beam epitaxy. It is observed that, for such nanowire LEDs, the peak quantum efficiency occurs at relatively high injection current levels of >100 A/cm², compared to those of conventional InGaN/GaN quantum well blue LEDs. Through detailed simulation studies, it is concluded that, Shockley-Read-Hall nonradiative recombination, due to the presence of surface states and defects, plays a dominant role on the nanowire LED performance. We have further shown that such nonradiative recombination can be greatly reduced when the nanowire LEDs are treated by ammonium sulfide solution ((NH ₄)₂S_x, 40-48% concentration), which can lead to a much faster increasing trend of quantum efficiency vs. injection current, compared to the unpassivated devices.