Speaker：GUO Wei,The Ningbo Institute of Industrial Technology (CNITECH) of the Chinese Academy of Sciences (CAS)
Time： Friday,2:00p.m.,29th March
Place： A718
Abastract:
Aluminum-gallium-nitride (AlGaN) alloys can emit light covering the spectrum from 210 to 360 nm, which can be widely used in solid state ultraviolet emitters. However, compared to InGaN-based blue LED counterpart, UV-LEDs still suffer from low external quantum efficiency (EQE) due to unsatisfied thin film quality, difficulties in p-type doping, strong TM polarization and many other challenges. In this talk, I will first talk about epitaxial growth of high Al composition AlGaN thin film on both sapphire and bulk AlN substrate via supersaturation control during MOC
VD growth. The benefits of using bulk AlN substrate in the application of UV-LED and UV laser diodes will be provided. I will mainly talk about polarity control scheme of III-nitride crystals and demonstrate a unique approach to enhancing the luminescence efficiency of AlGaN based multiple quantum wells (MQWs) and UV-LEDs via the introduction of a lateral-polarity structure (LPS) comprising both III- and N-polar domains on a single wafer. Enhanced luminescence intensity and internal quantum efficiency are demonstrated in LPS-based UV-MQWs, which could be explained by the secondary carrier injection in the three-dimensional band diagram with much reduced quantum-confined stark effect (QCSE). Finally, I will briefly talk about techniques in improving light extraction efficiency of UV-LEDs through photonic crystal patterning, and surface plasmon polariton (SPP) modulation.
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