Enhancing reliability of InGaN/GaN light-emitting diodes by controlling the etching profile of the current blocking layer

Abstract

SiO2 was used as the current blocking layer (CBL) during fabricating the InGaN/GaN-based light-emitting diodes (LEDs). The SiO2 film was prepared by plasma enhanced chemical vapor deposition (PECVD) at a lower temperature (LT) of 180 °C and a higher temperature (HT) of 280 °C for characterizing the reliability of LEDs. The degradation of output power in LT-CBL LED is as high as 6.8% during 1000 h in the high-temperature and humidity (85 °C/85 RH) condition. Experimental results demonstrate the low temperature grown CBL forms a larger side-wall angle via wet etching. The thinner side-wall ITO film cracks and the current spreading effect is suppressed, causing drastic power degradation. On the contrary, the HT-CBL SiO2 demonstrates optimal step coverage of ITO film for current spreading and then the HT-CBL LEDs slightly degrade as low as 5% in the accelerated reliability test. A dense quality of HT-CBL SiO2 as well as a good CBL decreased parasitic optical absorption in the p-pad electrode and p-finger. Besides, the HT-CBL SiO2 showed a small side-wall angle of 40˚ which increased the step coverage and current spreading of ITO. An approach is conducted to confirm the side-wall profile of CBL for each process.