Study on 3D thermal transport in micro-LEDs on GaN substrate at the level of kW/cm2

In this work, different sizes of micro-light-emitting diodes (μLEDs) were fabricated on the sapphire and GaN substrates. The thermal characteristics of μLEDs were studied by the forward voltage method, thermal transient measurement, and infrared (IR) thermal imaging. The μLEDs on the GaN substrate showed an approximately 10°C lower junction temperature and smaller amplitude of the K factors than those on the sapphire substrate under the current injection level of 4 kA/cm2. IR thermal imaging results showed the uniform temperature distributed on the GaN substrate. The thermal transient measurement showed that the thermal resistances of the mesa, epilayer, and the interface of GaN/substrate were reduced significantly for μLEDs on the GaN substrate. This means that a high-quality GaN crystal and homogeneous interface corresponded to little scattering for phonons. The APSYS simulation indicated that the high thermal and electrical conductivity of the GaN substrate played a key role in the low junction temperature and uniform temperature distribution. A small-sized μLED combined with a GaN substrate can become a perfect candidate for high-power applications and visible light communication.