紫外光氧化鋅奈米結構發光二極體之研究

Investigation of ultraviolet ZnO nanostructure light emitting diodes

盧姿君(Tzu-Chun Lu)

指導教授 ： 黃建璋

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.02176

摘要

近年來，氧化鋅相關材料及氮化鎵奈米結構由於其良好的材料特性，被廣泛的運用於短波長發光元件。但製作高純度之近紫外光氧化鋅同質接面發光二極體仍受到材料方面的諸多限制，如缺乏高穩定度的p型氧化鋅及大量的本質缺陷存在於氧化鋅內部，導致其相關元件之發光頻譜往往會伴隨著顯著的缺陷放光並降低近紫外波段之發光效率。為了解決上述之問題，p型氮化鎵由於與氧化鋅具有相同之晶體結構及相似之晶格常數，已被大量的運用於氧化鋅發光二極體之製作。而更有研究團隊利用原子層沉積鍍膜(atomic layer deposition)、脈衝雷射蒸鍍技術(pulse laser deposition)及有機金屬氣相沉積 (metal-organic chemical vapor deposition)等磊晶技術成長高品質氧化鋅薄膜，克服氧化鋅發光二極體缺陷發光之問題，但其高成本及耗時等缺點，依然有待解決。
　　為改善氧化鋅發光二極體在短波長範圍發光效率不顯著、缺陷發光以及高成本製作之問題，本論文提出一製程簡單、低溫且成本低廉之方式製作出氧化鋅奈米結構發光二極體，並提出適當設計的元件結構，使載子得以侷限在氧化鋅發光層，期望成功增強元件在紫外光波段之放光的同時且大幅降低缺陷影響，使純度最高的紫外光發光二極體得以實現。
本文中將會透過加入最佳化設計之二氧化矽/氧化鋅/二氧化矽載子侷限結構，並使用射頻磁控濺鍍 (RF magnetron sputtering) 製作一大面積低成本且高純度紫外光之ｎ型氧化鋅/p型氮化鎵異質接面發光二極體。傳統的氧化鋅異質ｐｎ接面發光二極體，其發光頻譜為400至700nm之寬頻光，是由於氮化鎵及氧化鋅內部之本質缺陷所造成；相反的，加入一二氧化矽載子侷限結構後，電子和電洞能夠更有效注入及被侷限在氧化鋅層內，使其發光頻譜峰值為氧化鋅放光之377nm並大幅降低缺陷發光。我們更提出在n型氧化鋅及p型氮化鎵介面做表面處理，此化學處理可大幅降低接面缺陷的產生，成功降低元件之缺陷發光，使紫外光波段放光顯著提升。
本文亦提出了具高光指向性之紫外光氧化鋅奈米柱發光二極體。藉由低溫的水熱法成長氧化鋅奈米柱於p型氮化鎵上，並在其介面加入一氧化鎂電子阻擋層，透過此結構之設計，電子能夠有效的被阻擋於氧化鋅側並與電洞結合，成功做出具有398nm近紫外光波段放光之奈米柱發光二極體。同時更進一步量測奈米柱在低溫之下之電激發光光譜，並對元件發光強度隨溫度下降而減弱以及波長峰值隨溫度變化而藍移之效應提出載子穿隧模型與溫度對能隙關係加以解釋。在光強度對角度變化量測方面,此元件也顯示出高度之光指向性且發散角為30度，此顯示我們不僅成功做出以氧化鋅奈米柱為發光源之發光二極體，且此奈米柱結構之氧化鋅發光元件更具有成為高指向性與高性純度紫外光發光元件之潛力。
　　我們成功提出利用低成本、低溫、製程簡單且可大面積製作之方法，利用射頻磁控濺鍍氧化鋅薄膜及水熱法成長氧化鋅奈米柱之方式製作出氧化鋅平面結構及奈米柱結構發光二極體，利用最佳化的結構設計以及有效的表面處理，載子得以有效被侷限在氧化鋅發光層，成功做出高純度且低缺陷放光之紫外光發光二極體。同時也製作出以氧化鋅奈米柱為發光源之發光二極體，並提出加入電子阻擋層之方式，使元件有效的放出此外光波段放光，具有高強度紫外光波段放光且低缺陷之氧化鋅奈米結構發光二極體將可實現。

關鍵字

紫外光發光二極體 ； 氧化鋅 ； 異質接面 ； 載子侷限結構 ； 奈米柱 ； 低溫電激光譜 ； 光指向性

並列摘要

ZnO related materials together with nanostructure LEDs have attracted great interests as the new short wavelength lighting source due to the superior optical and electrical characteristics of ZnO. For there are still difficulties in realizing ZnO homojunction LEDs, GaN is the most suitable substitute for p type material due to many of the physical properties are similar to ZnO. Many groups make effort to fabricate ZnO/p-GaN heterojunction LEDs, but how to suppress the defect related emission and thus achieve high purity ultraviolet (UV) light emission from ZnO are still under concerned.
To overcome these problems, we demonstrate ZnO/p-GaN LEDs with high quality ZnO thin film by RF sputtering at room temperature together with the post annealing. Asymmetric SiO2 confinement barriers of properly designed with ZnO in between are then carried out to exhibit UV radiative recombination in the ZnO layer. Moreover, by improving the interface of ZnO and p-GaN using surface treatments, the UV light emission with suppressing defect states from simple ZnO/p-GaN heterostructures without any confinement layers can be further realized.
For the superior physical properties of nanostructures, ZnO nanowire/p-GaN LEDs are also fabricated using hydrothermal synthesis for the single crystal ZnO nanowire arrays growth. MgO blocking layer between ZnO nanorod and p-GaN are inserted to enhance the UV emission from ZnO nanowires. Furthermore, the “inverted triangle” profile is formed due to the deposition of SiNx on ZnO nanorods. This special shape of nanorod arrays not only makes the continuous contact but also suppresses the deep level emission. We further extract the UV emission under low temperature, the luminescence together with the temperature effect are also discussed.
All the results mentioned above lead us to realize pure UV emission with great suppressed defect band in both ZnO thin film/p-GaN LEDs and ZnO nanowire/p-GaN LEDs. With low cost, low temperature, easily fabrication method and properly designed of structures, ZnO based LEDs indeed have great potential to become the UV light sources.

並列關鍵字

UV light emitting diodes ； ZnO ； carrier confinement structure ； nanorod ； low temperature electroluminescence

參考文獻

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