In this study, GaN-based flip-chip parallel micro light-emitting diode (μLED) arrays have been fabricated. Compared to a single LED with the same active region area, flip-chip parallel μLED arrays are superior on both modulation bandwidth and light output because of the uniform current spreading, improved heat dissipation, and higher light extraction efficiency. With this structure, an injected current density up to 7900 A/cm<sup>2</sup> has been achieved with a modulation bandwidth of ∼227 MHz. Meanwhile, the optical power is above 30 mW, which is more suitable for visible light communication in free space. The influence of resistance-capacitance (RC) time constant and carrier lifetime on the modulation bandwidth of parallel μLED arrays has also been investigated in details. This study will help the design of GaN-based LEDs to both enhance the modulation bandwidth and optical power.
In this study, we quantitatively investigate the influence of phosphor to the thermal properties of white LEDs.
We find that although the junction temperature of white LEDs is higher than corresponding blue LEDs, due to the high
thermal conductivity of the phosphor, it will help to improve the thermal dissipation and lower the thermal resistance of
white LEDs. Based on this, a heat transfer model has been proposed, which has also been confirmed by simulation
analysis. While for white LEDs with remote phosphors, although the lower junction temperature can help to improve
performance and reliability, the thermal resistance has not been improved. The heat generated by phosphors is isolated by
the silicone and this would increase the phosphor temperature and lead to a different degradation mechanism after a long