  In this work we present a detailed analysis of the interplay of Coulomb
effects and different mechanisms that can lead to carrier localization effects
in c-plane InGaN/GaN quantum wells. As mechanisms for carrier localization we
consider here effects introduced by random alloy fluctuations as well as
structural inhomogeneities such as well width fluctuations. Special attention
is paid to the impact of the well width on the results. All calculations have
been carried out in the framework of atomistic tight-binding theory. Our
theoretical investigations show that independent of the here studied well
widths, carrier localization effects due to built-in fields, well width
fluctuations and random alloy fluctuations dominate over Coulomb effects in
terms of charge density redistributions. However, the situation is less clear
cut when the well width fluctuations are absent. For large well width (approx.
> 2.5 nm) charge density redistributions are possible but the electronic and
optical properties are basically dominated by the spatial out-of plane carrier
separation originating from the electrostatic built-in field. The situation
changes for lower well width (< 2.5 nm) where the Coulomb effect can lead to
significant charge density redistributions and thus might compensate a large
fraction of the spatial in-plane wave function separation observed in a
single-particle picture. Given that this in-plane separation has been regarded
as one of the main drivers behind the green gap problem, our calculations
indicate that radiative recombination rates might significantly benefit from a
reduced quantum well barrier interface roughness.
