Unraveling the "Green Gap" problem: The role of random alloy fluctuations in InGaN/GaN light emitting diodes

TL;DR

This paper investigates the physical causes of the green gap in InGaN/GaN LEDs, revealing that random alloy fluctuations lead to decreased radiative recombination efficiency at higher Indium contents, limiting green light emission.

Contribution

The study uses atomistic simulations to identify alloy fluctuations as a key factor in the green gap of InGaN/GaN LEDs, providing new insights into their efficiency limitations.

Findings

Random Indium fluctuations reduce radiative recombination at higher Indium levels.

The green gap is partly due to decreased radiative efficiency caused by alloy disorder.

Understanding this mechanism can guide improved LED design for better green light emission.

Abstract

White light emitting diodes based on III-nitride InGaN/GaN quantum wells currently offer the highest overall efficiency for solid state lighting applications. Although current phosphor-converted white LEDs have high electricity-to-light conversion efficiencies, it has been recently pointed out that the full potential of solid state lighting could be exploited only by color mixing approaches without employing phosphor-based wavelength conversion. Such an approach requires direct emitting LEDs of different colors, in particular in the green/yellow range ov the visible spectrum. This range, however, suffers from a systematic drop in efficiency, known as the "green gap", whose physical origin has not been understood completely so far. In this work we show by atomistic simulations that a consistent part of the "green gap" in c-plane InGaN/GaN based light emitting diodes may be attributed to a decrease in the radiative recombination coefficient with increasing Indium content due to random fluctuations of the Indium concentration naturally present in any InGaN alloy.