Impact of random alloy fluctuations on the carrier distribution in multi-color (In,Ga)N/GaN quantum well systems
Résumé
The efficiency of (In,Ga)N-based light emitting diodes (LEDs) is limited by the failure of holes to evenly distribute across the (In,Ga)N/GaN multi-quantum well stack which forms the active region. To tackle this problem, it is important to understand carrier transport in these alloys. In this work, we study the impact that random alloy fluctuations have on the distribution of electrons and holes in such devices. To do so, an atomistic tight-binding model is employed to account for alloy fluctuations on a microscopic level and the resulting tight-binding energy landscape forms input to a quantum corrected drift-diffusion model. Here, quantum corrections are introduced via localization landscape theory. Similar to experimental studies in the literature, we have focused on a multi-quantum well system where two of the three wells have the same In content while the third well differs in In content. By changing the order of wells in this ‘multi-color’ quantum well structure and looking at the relative radiative recombination rates of the different emitted wavelengths, we (i) gain insight into the distribution of carriers in such a system and (ii) can compare our findings to trends observed in experiment. We focus on three factors and evaluate the impact that each have on carrier distribution: an electron blocking layer, quantum corrections and random alloy fluctuations. We find that the electron blocking layer is of secondary importance. However, in order to recover experimentally observed features – namely that the p-side quantum well dominates the light emission – both quantum corrections and random alloy fluctuations should be considered. The widely assumed homogeneous virtual crystal approximation fails to capture the characteristic light emission distribution across a multi-quantum well stack.
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