Localization Contrast As a Fundamental Limit of Radiative Quantum Efficiency
Disorder can localize valence- and conduction-band states to different degrees, yet whether such localization contrast has observable consequences remains poorly understood. Here, we show that localization contrast strongly impacts competing carrier-recombination channels. We illustrate this behavior in random In$_x$Ga$_{1-x}$N alloys. Increasing the In content from $x=13.5\%$ to $x=22\%$ progressively localizes the valence-band maximum state while leaving the conduction-band minimum state comparatively delocalized. This contrasting localization decreases the interband optical momentum matrix element underlying radiative recombination. For Auger-Meitner recombination, however, localization alone does not determine the coupling; atomic-scale disorder also breaks primitive-cell translational symmetry and modifies the momentum-space and phase structure of the states. This generates additional low-$Q$ components and enhances the Auger coupling by more than five orders of magnitude relative to pristine GaN. Thus, we provide a microscopic explanation for the competing trends in radiative and Auger recombination. More broadly, our results establish localization contrast as a mechanism through which disorder can control optical and carrier-carrier interactions in semiconductors.