Nonradiative Recombination Mechanism in Phosphor-Free GaN-Based Nanowire White Light Emitting Diodes and the effect of Ammonium Sulfide Surface Passivation

Abstract

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/cm 2 , 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 ) 2 S x , 40-48% concentration), which can lead to a much faster increasing trend of quantum efficiency vs. injection current, compared to the unpassivated devices.

An enhanced surface passivation effect in InGaN/GaN disk-in-nanowire light emitting diodes for mitigating Shockley–Read–Hall recombination

“…Moreover, the existence of surface states/defects leads to the slow increasing trend with current and peak quantum efficiency at high injection current. 21,41 We have also reported the passivation of GaN nanowire with (NH4)2Sx to improve photoluminescence and reduce the p-contact resistance of the devices. 31,32 It is noted that sulfides are widely used for the surface passivation of III-V semiconductors by forming strong bonds between the sulfur atoms and surface atoms in InP, 33,34 GaAs, 35,36 and InAs.…”

Enhanced Optoelectronic Performance of a Passivated Nanowire‐Based Device: Key Information from Real‐Space Imaging Using 4D Electron Microscopy

“…In InGaN, one of the most important semiconductor NW systems currently in use, nonradiative Shockley–Read–Hall (SRH) recombination at the surface defect states may arise from the presence of Ga/In dangling bonds, nitrogen vacancies, and/or incorporated oxygen . The presence of surface states may pin the Fermi level at the surface, causing band bending that decreases the density of free electrons toward the surface .…”

“…Different techniques have been employed to passivate surface states, including growing large bandgap AlGaN shells and treating the surface with sulfur‐containing compounds, such as (3‐mercaptopropyl)trimethoxysilane or (NH 4 ) 2 S . Very recently, Zhao et al reported the use of octadecylthiol (ODT) to efficiently passivate the surface dangling bonds and weaken the band bending of an InGaN/GaN quantum‐disk (Qdisk)‐in‐nanowire LED, significantly enhancing the steady‐state photoluminescence (PL) efficiency and external quantum efficiency (EQE) .…”

Unleashing the potential of molecular beam epitaxy grown AlGaN-based ultraviolet-spectrum nanowires devices

“…Mi's group used ammonium sulfide to increase the quantum efficiency of the InGaN-based white-light NWs-LEDs in an effort to reduce the nonradiative recombination centers. 147 The surface states' passivation in NWs has also been reported in GaAs, 148 InAs, 149 and InP 150 as it replaces the surface oxide while creating an In-S bond, hence reducing the mid-gap states. Also, by treating AlGaN-based UV NWs-LED using a KOH solution over a 40-s period, we observed an improvement in PL intensity by ∼80% compared with an untreated sample.…”