Modeling defect mediated color-tunability in LEDs with Eu-doped GaN-based active layers

Color tunability from red to orange to yellow has been demonstrated in GaN-based LED devices with Eu-doped GaN layers as the active region. Under current injection, this is achieved by varying the current density and the pulse conditions. The underlying mechanism behind this color tunability is a redistribution of energy among the 5DJ states of a Eu3+ ion. This energy shuffling is facilitated by a local defect that has been neglected in previous modeling work. Including this defect allows for a quantitative prediction of the relative time-averaged populations of the Eu3+ ion's 5D0 and 5D1 states. Extracting, from experimental results, the red and yellow/green emission spectra due to radiative transitions from the respective levels and mixing them allows the overall chromaticity of the emission to be determined for varied excitation conditions. In addition, the model allows us to determine the optimal injection conditions to maximize the gamut of color tunability while minimizing power consumption. These simulations pave the way for practical, systematic color tuning from a single-contact pixel.