利用應力工程達成可調式發光波長奈米環氮化镓多重量子井發光二極體

Abstract

以c軸的藍寶石基板來成長的氮化鎵發光二極體，有著嚴重的量子侷限史托克效應(Quantum Confined Stark Effect)，使其內部量子效率降低、輻射複合速度變慢以及發光波長紅移。在本論文當中，利用了多重物理耦合軟體(COMSOL)模擬了應變與量子侷限史托克效應的關係，且證明奈米環結構可有效降低量子侷限史托克效應，並利用奈米小球微影技術成功製作出奈米環氮化鎵多重量子井發光二極體，釋放了在多重量子井當中的應變，有效降低了量子侷限史托克效應，並透由改變奈米環的寬度，釋放不同的應變，達到可調變發光波長的發光二極體，可望用在微型顯示器上以及提升可見光通訊的頻寬。 第一章的內容包含發光二極體的優點、發光二極體的應用、三族氮化物(III-nitride materials)的優點以及量子侷限史托克效應的介紹。並回顧前人們解決量子侷限史托克效應的相關文獻以及使用奈米環結構的優點。 第二章主要陳述本研究中發光二極體的相關理論，其中包含外部量子效率、內部量子效率、光萃取效率的定義以及量子侷限史托克效應的屏蔽效應理論。 第三章主要陳述本研究中所使用到的模擬軟體、製程設備，其中包含多重物理耦合軟體、有限差分法軟體、奈米小球微影技術、電感耦合式乾蝕刻系統。 第四章的內容包含製程、模擬、光性以及電性的量測結果與討論。在光性的(i)光致激發(Photoluminescence)，量測到奈米環相較未做結構前的發光二極體最多有39nm的藍移，(ii)變功率的光致激發量測(Power dependent photoluminescence)，發現了QCSE的屏蔽效應減緩，(iii)低溫的時間解析光致激發(Time-resolved photoluminescence)中，發現載子壽命下降了10.5ns。在電性的(i)電致激發(Electroluminescence)，量測到奈米環相較未做結構前的發光二極體最多有55nm的藍移。 第五章主要陳述本研究的結論以及未來方向。

The conventional GaN-based LEDs grown on c-plane sapphire suffers from Quantum Confined Stark Effect (QCSE), which reduces the internal quantum efficiency, radiative recombination rate and red-shift of emission wavelength of the LEDs. In this work, the relation between strain and QCSE was simulated by COMSOL Multiphysics software and also prove that the nano-ring structure LEDs can reduces QCSE effectivity. Furthermore, the tunable strain relaxation in GaN/InGaN MQW LEDs by using the nano-ring structure was demonstrated through the nano-sphere lithography, and consequently achieve tunable emission wavelength LEDs. The nano-ring LEDs pave the way for applying in nano-display pixel and multi-channel visible light communication (VLC) system. The content of chapter 1 includes the advantage of LEDs, application of LEDs, advantage of III-nitride materials and introduction of QCSE. Then, review literature on methods of reduces QCSE as well as the advantage of using the nano-ring structure. Chapter 2 depicts the related theories of LEDs in this work. It includes the definition of external quantum efficiency, internal quantum efficiency, light extraction efficiency and the theory of screening effect of the QCSE. The simulation software, experiment equipment and measuring principle in this work were described in Chapter 3. It includes COMSOL Multiphysics software, lumerical FDTD software, nano-sphere lithography, Inductively Coupled Plasma-Reactive Ion Etching (ICP-RIE) system. The simulation, experiment, optical and electrical characteristics measurement results and discussions were presented in chapter 4. In optical characteristics, (i) Photoluminescence demonstrate blue-shift 39nm of emission wavelength of nano-ring LEDs compared with reference. (ii) Power dependent photoluminescence demonstrate screening effect of the QCSE was reduced. (iii) Time-resolved photoluminescence represent the carrier lifetime was reduced by 10.5ns. In electrical characteristics, (i) Electroluminescence demonstrate blue-shift 55nm of emission wavelength of nano-ring LEDs compared with reference. The content of chapter 5 depict the conclusions and future work.