Fabricated the High Brighness Light Emitting Diodes Through the Photoelectrochemical Wet Etching.

在本論文中，利用光輔助電化學濕式蝕刻作用於氮化銦鎵發光二極體結構，將平台側壁上蝕刻出三角形的孔洞、晶粒狀的粗化結構及奈米等級的三角錐，藉由快速側蝕所形成的三角形的孔洞可以減少光在發光層中的反射吸收更可以改善發光二極體的出光量。而隨著蝕刻時間的增加，側壁結構將由晶粒狀粗化結構變為奈米級的三角錐孔洞，有效提升發光元件之外部量子效率，並在側向光強度有5.9倍提升，此光輔助電化學蝕刻可有效提升發光二極體之發光效率。 在製作奈米級倒角錐體氮化銦鎵發光元件結構上，在經過4小時的電化學蝕刻處理後，在蝕刻平台上可觀察到大量奈米級倒角錐體結構，其幾何尺寸為高：184nm和基底寬度：245nm之倒角錐體結構，底部形成約10nm直徑之氮化銦鎵奈米盤結構，其形成機制可由發光層選擇性側向蝕刻和N-face蝕刻所組成，並根據Wulff理論，蝕刻穩定面是由最小表面積和表面能所組成，在氮化銦鎵量子井發光層之光激螢光光譜中，發現發光波長由476.9 nm藍移到434.8 nm，此42.1nm藍移量形成原因為：(1).氮化銦鎵量子井中壓電場效應因應力釋放而被減低，(2).倒角錐結構底部形成氮化銦鎵奈米盤結構而產生量子侷限效應，此角錐體保留P-GaN、MQW和N-GaN磊晶層結構，可以利用此種結構製造出奈米級發光元件。The higher light extraction efficiency of InGaN-based light emitting diodes (LED) has fabricated and study in this thesis. The fabricated InGaN-based LED wafers are treated through a photoelectrochemical (PEC) wet etching process using the Hg lamp illumination and KOH solution. The selected wet etching process of InGaN/GaN MQW layer was observed from the mesa sidewall between the p-type and n-type GaN interface with 4.2 µm/hr lateral etching rate. After 30 min PEC wet etching process, the light output power of the PEC etching LED had 2.04, 5.94, and 1.73 times enhancement measured from the from-side, lateral, and back-side direction compared with the standard LED. The phenomenon of higher light enhancement was caused by forming the triangle-shaped air holes located at the active layer region, grain-like roughening surface and nano-scale triangle pits on the mesa sidewall. Small sized self-assembled inverted hexagonal pyramids of InGaN structures were formed during the 4hr PEC etching. We define the pyramid forming mechanism included lateral selective etching and N-face etching. The photoluminescence (PL) intensity of GaN:Mg peak has a great enhancement caused by nano-scale pyramids. By comparing with the intensity ratio of GaN:Mg to GaN bandedge peaks at 12K, the ratios are 0.33 for standard LED and 8.1 for PEC wet etching LED. Due to the nano-cavity confined effect and the total reflecting effect of this inverted hexagonal pyramid structure, a stronger PL emission peak GaN:Mg was found. The PL emission peaks of InGaN/GaN MQW structure are located at 476.9nm for standard and 434.8nm for etched sample, a strong blue shift phenomenon (42.1nm) was observed caused by reduced the piezoelectric field. The quantum confinement effect and compress strain relaxation are observed from temperature-dependent PL spectrum. This inverted hexagonal pyramids consisted with p-type GaN:Mg, nano-disk InGaN/GaN active layer, and n-type GaN:Si layer are suitable for the nano-scale optoelectric devices.摘要…………………………………………………………………………………… i Abstract……………………………………………………………………………… ii 總目錄……………………………………………………………………………… iii 圖目錄………………………………………………………………………………… v 第一章 序論…………………………………………………………………………… 1 1.1 前言………………………………………………………………………… 1 1.2 簡介及文獻回顧…………………………………………………………… 3 1.3 研究動機…………………………………………………………………… 5 第二章 原理…………………………………………………………………………… 7 2.1 光輔助電化學蝕刻氧化法………………………………………………… 7 2.1.1 直接能隙(direct bandgap)與間接能係(indirect bandgap)… 7 2.1.2 光激發電子電洞…………………………………………………… 7 2.1.3 光輔助電化學蝕刻氧化法………………………………………… 8 2.2 蝕科技術…………………………………………………………………… 10 2.2.1 濕式蝕刻…………………………………………………………… 10 2.2.2 乾式蝕刻…………………………………………………………… 10 2.2.3 氮化鎵與蝕刻溶液的關係………………………………………… 11 第三章 實驗儀器設備……………………………………………………………… 20 3.1 製成儀器…………………………………………………………………… 20 3.1.1 光輔助電化學蝕刻氧化裝置……………………………………… 20 3.2 分析儀器…………………………………………………………………… 20 3.2.1 光激發螢光光譜(Photoluminescence)………………………… 20 第四章 氮化鎵發光二極體之蝕刻氧化反應……………………………………… 27 4.1 氮化鎵材料之蝕刻氧化反應……………………………………………… 27 4.1.1 試片清洗步驟……………………………………………………… 27 4.2 似次波長光柵(Sub-Wavelength Grating like)與側壁粗化(Sidewall Roughness)光亮度提升效應…………………………………………………… 29 4.2.1 文獻回顧………………………………………………………………… 29 4.2.2 試片製備及實驗過程……………………………………………… 32 4.2.3 結果與討論………………………………………………………… 32 4.2.4 結論………………………………………………………………… 34 4.3 鎂摻雜氮化鎵(GaN:Mg)倒六角錐結構(Hexagonal Inverted Pyramids)35 4.3.1 文獻回顧…………………………………………………………… 35 4.3.2 試片製備及實驗過程……………………………………………… 35 4.3.3 結果與討論………………………………………………………… 36 4.3.4 結論………………………………………………………………… 38 第五章 結論與未來展望…………………………………………………………… 58 5.1 結論………………………………………………………………………… 58 5.2 未來展望…………………………………………………………………… 59 5.2.1 製作鎂摻雜氮化鎵(GaN:Mg)倒六角錐發光元件………………… 59 5.2.2 PEC濕式平台蝕刻(mesa etching)應用於氮化鎵發光二極體… 59 參考文獻……………………………………………………………………………… 6