Influence of random alloy fluctuations in InGaN/GaN quantum wells on LED efficiency

In this work we present how compositional fluctuations in the InGaN alloy in InGaN/GaN quantum wells (QWs) influence the strengths of optical transitions and hence LED efficiency. Using atomistic empirical tight-binding simulations we show that random alloy fluctuations lead to statistical spread of the momentum matrix elements and the emission energy, and that the two quantities are correlated for the ground state transitions. These fluctuations can be related to lateral fluctuations of the electronic states and quantum confined Stark effect. From simulations on statistical sets of random samples for different Indium concentrations, we extract mean “macroscopic” emission spectra. The behaviour of the ground state transition momentum matrix elements with Indium content is found to correlate well with experimentally extracted spontaneous recombination parameters. A systematic reduction of these matrix elements with respect to results obtained without considering alloy fluctuations suggests that standard simulation models based on homogeneous media may overestimate LED efficiency by roughly 10%. A qualitatively different behaviour between flat band QWs and QWs with strong quantum confined Stark effect is found and explained by the localization behaviour of electrons and holes.