  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.
