Efficiency Enhancement of 280-Nm Uvc Led via High-Conductive High-Transparent P-Type Al0.5ga0.5n

This project is to continue the collaboration between NCU and Tekcore Inc., and boost the output power of 283-nm UVC LED from 2.12 mW to 5 mW. The development of UVC LED is challenged by two technique obstacles: i) High-quality AlN epitaxial layer. ii) High-transmissive, high-conductive p-type AlGaN. Our previous team work with Tekcore had overcome the 1st obstacle with a unique epitaxial growth method, which can produce high-quality AlN in a cost-effective way and has been implemented in Tekcore’s epitaxy facilities. Compared to the 1st one, the 2nd technique obstacle is often regarded as the more difficult one. This is due to the trade-off between high-transmission and high-conductivity in p-type AlGaN. The hole activation energy in wide-bandgap material is inherently high, leading to the low free hole concentration. Although the concentration can be increased with a reduced bandgap, the high optical absorption in the p-type layer can severely sacrifice the output power. This is the main reason leading to the very low (< 10%) external quantum efficiencies (EQE) of UVC LEDs to date. To address the issue, we plan to adopt the AlxGa1-xN/AlyGa1-yN superlattice, obtained with a pulsed gas injection technique, to increase the incorporation efficiency of Mg (the p-type dopant) in AlGaN. Interrupting the supply of carrier gas is expected to promote the bonding between Mg and nitrogen precursors, and thus results in increased hole concentration. The superlattice is to be integrated with Ni/Al-based ohmic contact to achieve the high-transmissive, high-conductive p-type Al0.5Ga0.5N epitaxial layer, with which we aim to enhance the efficiencies of carrier injection and light extraction of UVC LEDs.