The effect of mesa length-width aspect ratio on the thermal performance of deep ultraviolet flip-chip micro-light-emitting diodes

The performance of deep ultraviolet micro-light-emitting diodes (DUV μLEDs) is severely limited by self-heating effects at high current densities, leading to efficiency droop and reduced operational lifetimes. In this work, the effect of the mesa LW-ratio, passivation layer materials, and p-pad design on heat dissipation for flip-chip μLEDs is systematically investigated. It is found that for conventional flip-chip μLEDs, an increased LW-ratio and the use of passivation layer materials with higher thermal conductivity can decrease the peak temperature of the chip but increase the total internal thermal energy within the chip. The primary reason is that these factors promote more heat dissipation toward the chip edge not toward the p-pad, resulting in a more uniform heat distribution within the chip and a deterioration of overall heat dissipation capability. Furthermore, for flip-chip μLEDs, we propose covering the inclined sidewall with the p-pad. As a result, both the peak temperature and the total internal thermal energy decrease as the LW-ratio increases because of the increased p-pad contact area with the increased LW-ratio. This study provides valuable insights into advancing the thermal management design of DUV μLEDs.