The recent breakthrough in high power GaN LED's efficiency makes the adoption of these tiny solid state light
emitting devices into general lighting application earlier than expected before. However, heat management is still an
important issue for these white high power GaN LEDs. So far, the most popular driving current for 1mm square die is
about 350mA but there is a trend to increase the driving current up to 1A or even higher. In order not to degrade the LED
performance at such a high current operation, it is very important to reduce the thermal resistance and keep the junction
temperature below 60 degree centigrade.
In the past, GaN flip chip, thin GaN LED, or GaN on SiC or GaN substrate are some typical structures used to
make high power LEDs with low thermal resistance. However, all of these methods need very complicated chip process
or using very expensive substrates and are difficult to meet general lighting dollar per lumen target. In this study, we
proposed a cheaper way to make a high power LED die with lower thermal resistance. We will report how we can
achieve the thermal resistance of high power GaN LED die less than 1°C/W.
The internal quantum efficiency (IQE) of commercial ultra high brightness AlGaInP red LED has already
reached 90% or higher but the light extraction efficiency was only about 30% to 50%. Through the improvement of
surface texturing structure by nano-imprint technology and current spreading by using narrow width ohmic contact
metal line, the light extraction efficiency of AlGaInP red LED was significantly improved up to 60%. In AlGaInN LED,
the thermal resistance of the LED chip can be reduced by thinning down or totally removing the sapphire substrate and
then replacing it by high thermal conductivity materials. Therefore, the performances of high power AlGaInN LED
chips were improved in high current density operation condition.