以氫化物氣相磊晶法成長氮化鎵厚膜於氮化鎵奈米柱之研究; Growth of Thick GaN Layers on GaN Nanorod Template by HVPE

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/48145

Title:	以氫化物氣相磊晶法成長氮化鎵厚膜於氮化鎵奈米柱之研究;Growth of Thick GaN Layers on GaN Nanorod Template by HVPE
Authors:	蕭羽珊;Yu-Shan Hsiao
Contributors:	光電科學研究所
Keywords:	氫化物氣相磊晶;氮化鎵;HVPE;GaN
Date:	2011-07-20
Issue Date:	2012-01-05 14:35:21 (UTC+8)
Abstract:	本論文主要研究氫化物氣相磊晶系統，利用本實驗室自組的水平式氫化物氣相磊晶系統(Hydride Vapor Phase Epitaxie, HVPE)成長氮化鎵厚膜，研究內容主要藉由調整不同的磊晶成長參數：1.使用不同載子氣體，2.改變載子氣體流量，3.改變三五族氣體流量比例，並透過光學顯微鏡(OM)、掃描式電子顯微鏡(SEM)、原子力顯微鏡(AFM)，以及量測單位面積缺陷數(EPD)等方式，對材料的表面特性及材料品質做分析。由本論文研究顯示，在全氫氣的環境下以及高五三比例的情況下可以成長出表面形貌平整的氮化鎵厚膜，且利用調整氣體的流量，可優化其膜厚均勻度，成長出膜厚均勻度佳的氮化鎵厚膜，本實驗由一開始較差的膜厚均勻度為91%，利用調整氣體流量後，得到膜厚均勻度為5%之氮化鎵厚膜，大幅改善了使用HVPE成長氮化鎵厚膜之膜厚不均勻的特性。由於Sapphire基板和氮化鎵材料的熱膨脹係數不同，造成強大的應力(stress)，使得磊晶成長的降溫過程中，氮化鎵厚膜和Sapphire基板產生碎裂(crack)。故利用黃光微影製程技術製作氮化鎵奈米柱，作為磊晶成長氮化鎵厚膜之基板以降低應力，成功成長出厚度大於350μm且不碎裂的氮化鎵厚膜，且表面形貌平整如MOCVD成長之氮化鎵薄膜，單位面積缺陷數也由傳統MOCVD成長之氮化鎵薄膜6.52×108 cm-2降低至2.00×107 cm-2，大約減少了30倍。所以結合氮化鎵奈米柱的製程技術及HVPE磊晶技術，不只提高了氮化鎵厚膜成長於藍寶石基板之最大厚度限制，更大幅提升了氮化鎵材料的品質。最後將不同厚度的氮化鎵厚膜/Sapphire基板應用於氮化鎵發光二極體元件(LED)，用MOCVD成長氮化鎵發光二極體結構，再利用黃光微影製程技術製作發光二極體元件，量測發光二極體元件之光電特性和熱特性。由於利用HVPE成長之氮化鎵厚膜提升了氮化鎵材料的品質，使得發光二極體元件之光輸出功率增加，另外也利用熱影像量測不同電流驅動下之發光二極體的熱分佈，由於氮化鎵材料之導熱特性佳，當氮化鎵磊晶層越厚時，發光元件的散熱效率比厚度薄時更容易將熱導出，因此改善了高電流注入下光輸出功率下降的結果，一般傳統LED大約在驅動電流設定為400mA時，光輸出功率就會開始下降，而使用125μm之氮化鎵厚膜製作之LED，在電流提升到700mA後，光輸出功率才會開始往下降。由此，使用氮化鎵厚膜/Sapphire基板作為發光二極體之磊晶基板，並製作發光二極體元件，可有效提升輸出的光功率以及改善元件熱效應的產生。 In this research, we used horizontal system of home-made hydride vapor phase epitaxy (HVPE) to growth thick GaN films on 2μm un-doped GaN/ sapphire substrate. We changed the growth parameters, for example, using different carrier gas, changing V/III ratio and carrier gas flow to optimize the crystal quality. Then we used optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM) to measure the surface morphology, the thickness of epitaxial layer, and the crystal quality. We could produce high quality thick GaN template that were lower defect density, mirror-like surface, and better thickness uniformity. Then we used thick GaN template to do GaN-based light-emitting diodes (LEDs). The crystalline quality of the epitaxial film could be improved by using thick GaN template. The light output power (LOP) of LED grown on 125μm GaN template was 136% higher than those of LED grown on 2μm GaN template at the injection current of 20mA, respectively. The saturation current of LED grown on 125μm GaN template was 670mA higher than those of LED grown on 2μm GaN template that was 400mA. These measured result was explained by thermal imager measurement in this article. Finally, in order to reduce the stress causing by heteroepitaxy, we used HVPE to successfully produce above 350μm thick GaN epitaxy on GaN nanorod template. The surface of 350μm thick GaN was mirror-like surface. Compared with EPD measurement of conventional 2μm GaN template and 350μm GaN template, the EPD was reduced from 6.52×108 cm-2 to 2.00×107 cm-2 by increasing the thickness of GaN epitaxial layer.
Appears in Collections:	[Graduate Institute of Optics and Photonics] Electronic Thesis & Dissertation

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