Zhang Shuang, Liu Yuan, Zhang Jun, Zhang Yi, Xu Linlin, Chen Qian, Dai Jiangnan, Chen Changqing
Opt Express. 2019 Sep 30;27(20):A1601-A1614. doi: 10.1364/OE.27.0A1601.
Optical polarization characteristics and light extraction behavior of deep-ultraviolet (DUV) light-emitting diode (LED) flip-chip with full-spatial omnidirectional reflector (FSODR) have been investigated. FSODR is fabricated to be simultaneously covered on the whole flip-chip, except the sapphire surface. It is found that the FSODR greatly enhance both transverse-electric (TE) and transverse-magnetic (TM) mode light extraction at every space angle, resulting in total enhancement of 73.1% and 79.8%, respectively. Moreover, the four individual ODR structures separated from FSODR, which are covered on the surface of n-AlGaN, the interface of p-GaN/p-AlGaN, the sidewall of mesa and the sidewall of n-AlGaN/AlN, respectively, show considerably different optical polarization characteristics and extraction behaviors between each other. The achievements of FSODR cannot be obtained by any separated ODR, and all of the individual ODRs can contribute to the FSODR. Especially, the synergy effect of TM extraction behavior obviously exists in FSODR. As a result, the light extraction efficiency (LEE) enhancement of FSODR is approximately 60% at a high current density of 140A/cm. This study is significant for understanding and modulating the extraction behavior of polarized light to realize high efficiency AlGaN-based DUV LEDs.
研究了具有全空间全向反射器（FSODR）的深紫外（DUV）发光二极管（LED）倒装芯片的光学偏振特性和光提取行为。FSODR被制作成除蓝宝石表面外同时覆盖整个倒装芯片。结果发现，FSODR在每个空间角度都极大地增强了横向电（TE）和横向磁（TM）模式的光提取，总增强分别达到73.1%和79.8%。此外，从FSODR分离出的四个单独的ODR结构，分别覆盖在n-AlGaN表面、p-GaN/p-AlGaN界面、台面侧壁和n-AlGaN/AlN侧壁上，彼此之间呈现出显著不同的光学偏振特性和提取行为。FSODR的成果无法通过任何单独的ODR获得，且所有单独的ODR都对FSODR有贡献。特别是，FSODR中明显存在TM提取行为的协同效应。结果，在140A/cm的高电流密度下，FSODR的光提取效率（LEE）提高了约60%。这项研究对于理解和调制偏振光的提取行为以实现高效的基于AlGaN的深紫外发光二极管具有重要意义。
