氮化物基板研製及氮化鎵材料磊晶成長

Abstract

本論文探討以有機金屬氣相沉積法成長氮化物材料，並研究其氮化物材料特性。研究內容主要針對氮化物基板之研製、氮化物材料磊晶成長以及發光二極體元件光電特性研究。首先，我們利用鎳金屬做為奈米尺寸的蝕刻遮罩，利用蝕刻製程研製出氮化鎵奈米柱基板，從SEM量測觀察出使用鎳金屬所研製的氮化鎵奈米柱尺寸為250nm~500nm，密度為3 × 108 cm-2。 從X-ray量測分析可知使用氮化鎵奈米柱基板可有效提升氮化鎵薄膜的品質，其GaN (102)面的半高寬可以從470sec 降至370sec。在藍光發光二極體方面，使用氮化鎵奈米柱基板之發光二極體可以提昇發光二極體的內部量子效率和光萃取效率。在順向20 mA電流注入下，對於元件光輸出功率可提升29.8%。 在提昇發光二極體的電流擴散方面，首先是先成長低阻值的高濃度 n型氮化鎵薄膜於氮化鎵奈米柱基板上，利用AFM和TEM量測高濃度n型氮化鎵的缺陷密度，觀察出氮化鎵奈米柱基板可以有效降低高濃度n型氮化鎵薄膜缺陷，其錯位缺陷密度可有效地從傳統使用低溫氮化鎵緩衝層和未摻雜氮化鎵~1.1 × 109 cm-2降低到3.9 × 108 cm-2。應用此高品質高濃度n型氮化鎵薄膜於藍光發光二極體結構中，可以有效降低其元件動態電阻以及提昇元件中的電流擴散長度，進而提高發光二極體元件的光輸出功率。在順向20 mA電流注入下，提昇電流擴散長度可以提昇14.8%元件光輸出功率。 於高深寛比圖案化藍寶石基板方面成功應用物理氣相沉積方式所研製氮化鋁緩衝層來成長高品質氮化鎵薄膜，分別探討使用物理氣相沉積方式研製氮化鋁緩衝層所成長氮化鎵薄膜於高深寛比圖案化藍寶石基板上的薄膜品質、晶格結構和磊晶成長機制。從X-ray和TEM分析可知使用物理氣相沉積氮化鋁緩衝層可以提升成長在高深寛比圖案化藍寶石基板的氮化鎵薄膜品質，其GaN (102)面的半高寬可以從339sec 降至249sec。在藍光發光二極體方面，使用物理氣相沉積氮化鋁緩衝層於高深寛比圖案化藍寶石基板可以提昇發光二極體元件的內部量子效率，進行增加其元件光輸出功率。在順向20 mA電流注入下，對於元件光輸出功率可提升46%。 在研製氮化鋁鎵基板研究上，結合奈米圖案化藍寶石基板和物理氣相沉積氮化鋁緩衝層可以有效降低缺陷的產生。從X-ray分析可知使用奈米圖案化藍寶石基板和物理氣相沉積氮化鋁緩衝層成長可以提升氮化鋁鎵薄膜的品質，其AlGaN (102)面的半高寬可以從782sec降至631sec；從光激發光量測和拉曼光譜分析觀察出氮化物薄膜成長於奈米尺寸間距的圖案化藍寶石基板，會因為薄膜的應力影響，故改變氮化物的發光波長，進而在PL量測結果顯示雙波峰現象。

In this dissertation, the fabrication of GaN nanorod template, the growth mechanism and characterization of GaN epitaxial layer grown on GaN nano rod template, and the characteristics of GaN-based LEDs prepared on GaN nano rod template have been studied. The improvement of current spreading in GaN-based LEDs with high quality Si-doped n-GaN prepared on GaN nanorod template is investigated. The mechanism and characterization of GaN grown on high aspect ratio patterned sapphire substrate (HARPSS) with physical vapor deposition (PVD) AlN nucleation layer and characteristics of GaN-based LEDs have been also studied. In addition, we also discuss the growth and characteristics of AlGaN grown on nano patterned sapphire substrate (NPSS) with PVD AlN nucleation layer. The primary results obtained in this dissertation are summarized as follow: (a) The uniform and high density GaN nano rods were fabricated by Ni nano mask. The diameter and density of GaN nano rods were around 250 nm~500 nm and 3 × 108 cm-2. In this dissertation, the GaN nano rod templates for epitaxial growth were fabricated by Ni mask. It was found that GaN epitaxial layer could directly grow on GaN nanorod template without buffer layer. It was also found that the GaN grown on GaN nanorod template showed narrower FWHM of GaN (102) in DCXRD (~370 sec), as compared with conventional GaN without GaN nanorod template. It was found that we can enhance LED output power by GaN nanorod template due to both increases internal quantum efficiency and light extraction efficiency, as compared with conventional LED. With 20 mA injection, the LED output power was enhanced by 29.8%, as compared with conventional LEDs. (b) For current spreading improvement in GaN-based LEDs, the GaN-based LED with high quality heavily Si-doped n-GaN prepared on GaN nanorod template was proposed and fabricated. It was found that we can reduce etching pits density in heavily Si-doped n-GaN epitaxial layer by using the GaN nanorod template (~3.9 × 108 cm-2), as compared to the conventional heavily Si-doped n-GaN without GaN nanorod template. It was found that we can enhance 14.8% LED light output power by improving current spreading with high quality heavily Si-doped n-GaN prepared on GaN nanorod template. (c) The high-quality GaN epitaxial layer grown on HARPSS with PVD AlN nucleation layer by metal organic chemical vapor deposition (MOCVD) have been studied. The growth mechanism and characterization of GaN epitaxial layer grown on HARPSS with different AlN nucleation layers have been studied. It was found that the GaN prepared on HARPSS with PVD AlN nucleation layer showed lower TDs and pure wurzite structure in TEM, as compared with GaN prepared on HARPSS with MOCVD grown AlN nucleation layer. The LEDs prepared on HARPSS with PVD AlN nucleation layer could enhance the 46% LED light output power, as compared with LED prepared on HARPSS with MOCVD grown AlN nucleation layer. (d) The AlGaN epitaxial layer prepared on nano patterned sapphire substrate with PVD AlN nucleation layer was proposed and fabricated. It was found that the AlGaN grown on NPSS with PVD AlN nucleation layer showed narrower FWHM of AlGaN(102) in DCXRD (~631sec), as compared with AlGaN prepared on planar sapphire substrate and PVD AlN nucleation layer. In addition, the formation of two peak phenomenon found in PL measurement for AlGaN prepare on NPSS was also discussed.