Modeling of color tunable light-emitting diodes with Eu-doped GaN active layers

It has been demonstrated that gallium nitride (GaN) based LED devices with active Europium-doped Gallium Nitride (GaN:Eu) layers can be tuned under current injection from red to orange to yellow. This tuning is achieved by changing current density under continuous excitation or by adjusting the duty cycle and amplitude of pulse-width modulated pulsed excitation. The underlying mechanism is a redistribution of energy among ⁵D_J states of the Eu³⁺ ion through energy shuffling that involves a local defect. This shuffling among different excitation states is possible due to the wide range in time scales (10ps to 200µs) of the relevant processes within this defect complex. To quantitatively model this behavior, we extended previous modeling work by including the local defect. As a result, we can predict red-yellow tunability by looking at the relative average populations of the Eu’s ⁵D₀ and ⁵D₁ states and using color mixing of red emission from the ⁵D₀ state with green emission from the ⁵D₁ state. Furthermore, by considering the defect as able to emit light in the blue spectral region, our model can predict tunability parameters within a larger color space due to the mixing of three distinct colors: red, green, and blue. A specific candidate for such a defect would be a Si-Mg complex.