Enhancement of light extraction efficiency in sub-300nm nitride thin-film flip-chip light-emitting diodes

• Published in: Solid-state electronics 2013-11, Vol.89, p.156-160
• Main Authors: Lachab, M., Asif, F., Zhang, B., Ahmad, I., Heidari, A., Fareed, Q., Adivarahan, V., Khan, A.
• Format: Article
• Language: English
• Subjects: AlGaN/AlGaN multiple quantum wells; Deep-UV LEDs; Laser lift-off; Light extraction efficiency
• ISSN: 0038-1101; 1879-2405
• DOI: 10.1016/j.sse.2013.07.010

•Enhancement of light extraction efficiency in 287nm thin-film flip-chip LEDs.•Substrate laser lift-off technique was used to fabricate the Deep-UV thin-film LEDs.•A 1.5-fold increase in the thin-film LED output power was achieved at 20mA using wet etching in KOH solution.•Devices encapsulation produced an additional 1.3-fold enhancement in the output power.•Optical properties of the epoxy encapsulant were stable at 20mA dc current injection. We report on the improved light extraction efficiency of 287nm small periphery AlGaN/AlGaN thin-film flip-chip (TFFC) light-emitting diodes (LEDs) fabricated using the laser lift-off technique. After sapphire substrate removal, the exposed AlN N-face was etched in a KOH solution. The result was a 1.5-fold increase in the TFFC device output power at 20mA dc current injection, which was attributed to the AlN surface texturing. TFFC die encapsulation process produced an additional 1.34-fold enhancement of the emitted light power. More importantly, the encapsulated thin-film LEDs exhibited a similar reliability performance compared to encapsulated conventional FC LEDs processed from the same epiwafer, and with no noticeable degradation of the encapsulating material optical properties.