  We present a detailed theoretical analysis of the electronic and optical
properties of c-plane InGaN/GaN quantum well structures with In contents
ranging from 5% to 25%. Special attention is paid to the relevance of alloy
induced carrier localization effects to the green gap problem. Studying the
localization length and electron-hole overlaps at low and elevated
temperatures, we find alloy-induced localization effects are crucial for the
accurate description of InGaN quantum wells across the range of In content
studied. However, our calculations show very little change in the localization
effects when moving from the blue to the green spectral regime; i.e. when the
internal quantum efficiency and wall plug efficiencies reduce sharply, for
instance, the in-plane carrier separation due to alloy induced localization
effects change weakly. We conclude that other effects, such as increased defect
densities, are more likely to be the main reason for the green gap problem.
This conclusion is further supported by our finding that the electron
localization length is large, when compared to that of the holes, and changes
little in the In composition range of interest for the green gap problem. Thus
electrons may become increasingly susceptible to an increased (point) defect
density in green emitters and as a consequence the nonradiative recombination
rate may increase.
