Mesa-size-dependent color contrast in flip-chip blue/green two-color InGaN∕GaN multi-quantum-well micro-light-emitting diodes

The authors fabricate blue/green two-wavelength, InGaN∕GaN quantum-well (QW), flip-chip micro-light-emitting diodes (μ-LEDs) of different mesa sizes by stacking QWs of different indium contents. It is found that the blue/green contrast ratio of such a μ-LED increases with the mesa size. The relatively stronger blue intensity in a device of a larger mesa area is due to its higher operation junction temperature such that hole migration can be enhanced through thermally exciting holes to escape from the QW (green emitting) closest to the p-type layer and to be captured by the neighboring QWs (blue emitting). The higher junction temperature in such a μ-LED of a larger mesa area is due to its smaller ratio of the sidewall surface area over the active volume, leading to the less effective sidewall heat radiation and light extraction.