Study On Optimization Of Reliability Of GaN-based LED Chips

In an conventional GaN-based light-emitting diode (LED), the heatgenerated at the light emitting portion could not be removed effectively. As aresult, the temperature of the device rises due to heat accumulation, whichaccelerates the deterioration of the LED chip.In this paper, a new LED structure has been studied, in which aprotecting layer is formed on the side wall of GaN-based LEDs. In this LEDstructure, the side wall surface of the LED is passivated and the heatdissipating ability is improved. Accelerated aging tests of LEDs withprotecting layer have been carried out at increased injection current level.Different insulating materials, such as Al2O3, AlN, and AlON are chosen forprotecting layer fabrication. The influence of the protecting layer on thereliability of the LEDs is studied by analyzing the variation of the outputpower over aging time. Experimental results show that output powerdecreases more slowly for GaN-based LEDs with protecting layer formed onthe side wall.In this paper, vertical structure GaN-based LEDs bonded on Si substrateare first fabricated and their accelerated aging behavior is tested. Protectinglayers of Al2O3, AlN, and AlON are then formed on the side wall of theconventional LEDs. Accelerated aging experiments are carried out at aninjection current level of20mA and50mA to compare the aging behaviors ofLEDs with different protecting layers.Experimental results show that there is an obvious slow down in theoutput power reduction over time for LEDs with AlON protecting layer,which proves that an AlON protecting layer improves the reliability of anLED chip. This is attributed to excellent thermal conductivity of AlON, whichhelps remove the heat from the active region of the LED. Meanwhile, theAlON protecting layer acts as an effective surface passivation, which reduces dangling bonds on the side wall of an LED and improves the reliability of thedevice.This work is believed to have a positive significance for improving thereliability of GaN-based LEDs and promoting further development ofsemiconductor lighting.