This project aims to improve the external quantum efficiency (EQE) of ultraviolet C (UVC: λ < 290 nm)LED via combining the concept of admittance diagram and the technique of metal-organic chemicalvapor deposition (MOCVD). One of the obstacles hampering EQEs of UV LEDs is the difficulty insimultaneously attaining high-quality and high-transmissive AlN/AlGaN interfaces, which are the mainstructures in UV LEDs. Since the optical refractive indices of AlN and AlGaN are determined by thegrowth conditions and Al-content, the index-mismatched AlN/AlGaN and AlN/sapphire (substrate)interfaces can exhibit very high reflectance, severely sacrificing light extraction efficiency of the device.To address issue, we plan to minimize the interface reflectance through the optimized admittancediagram. The optimized process is based on our unique MOCVD technique that can deliver high-qualityAlN and n-type Al0.6Ga0.4N with single growth temperature and pressure, rendering single optical refractiveindices. The thickness of the high-quality AlN can be up to 3.2-μm, while the electron mobility of then-type Al0.6Ga0.4N is as high as 58.3 cm2/V-s, both of which serve as the corner stones for UVC LEDs.According to preliminary analyses, the device with optimized interface structures exhibits the lightextraction efficiency enhancement of 15% at the incident angle of 0º, and the enhancement increases withlarger incident angles.Minimizing interface reflectance via optimized admittance diagram is believed as an effective approachto improve the EQEs of UVC LEDs.
|Effective start/end date||1/08/17 → 31/07/18|
In 2015, UN member states agreed to 17 global Sustainable Development Goals (SDGs) to end poverty, protect the planet and ensure prosperity for all. This project contributes towards the following SDG(s):