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標題: Fabrication and Characterization of Low-Dislocation-Density GaN Epilayers on Sapphire Substrates
作者: 吳學維
Wu, Hsueh-Wei
關鍵字: Dislocation;差排;Etch-pit;Patterned sapphire substrate;蝕刻孔穴;圖案化藍寶石基板
出版社: 材料科學與工程學系所
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Material properties of GaN epilayers grown on the wet-etched protruding, truncated and invert-pyramidal recessing patterned sapphire substrates (PSSs) as well as planar substrates , are in detail investigated, along with its relationship to their optical characterization. High-resolution x-ray diffraction (XRD) results reveal different dislocation configurations on the PSSs. The scanning electron microscopy images show that the etched pits in the case of the invert-pyramidal recessing PSS exhibit a regular distribution, less etched pits densities (EPDs) or threading dislocation densities onto the recessing pattern area than those onto the sapphire mesas. While no regular distribution for the etched pits onto the former is observed. Additionally, crystal quality of the GaN grown onto the invert-pyramidal recessing PSS is better than that onto the protruding PSS. The screw and edge dislocation density of GaN grown onto the invert-pyramidal recessing PSS is about 107 and 108 cm-2 (common 109 cm-2) respectively determined by etched pits method. The calculated density is a little lower than that derived from the XRD method. The reason to interpret this difference is proposed in this study. From photoluminescence (PL) spectra, the GaN grown onto the invert-pyramidal recessing PSS exhibits the narrowness among all GaN epilayers grown the four substrates mentioned above. Moreover, we demonstrate a tendency that the PL integrated intensity of all GaN epilayers decreases with an increment of the density of the dislocations with edge component. The results indicate that the edge-type dislocations act as the dominant nonradiative centers in GaN epitaxial layers.
These results could reflect that the GaN grown on the invert-pyramidal recessing PSS is a much better template for the regrowth of GaN using a maskless technique as compared with the protruding PSS. The GaN after regrowth shows that EPDs associated with screw dislocation are around 7.3 105 cm-2 and those with edge dislocations are around 3.1 106 cm-2. As compared with the GaN directly grown onto the invert-pyramidal recessing PSS, the EPDs corresponding to edge dislocations of the regrown GaN on this template decrease a factor of two orders (from 108 cm-2 to 106 cm-2).

本論文主要研究氮化鎵磊晶膜成長於一般藍寶石基板和凸形、凹形、倒金字塔凹形圖案化藍寶石基板之材料特性,並探討材料特性與光學特性之關係。我們經由高解析雙晶繞射結果顯示出不同差排型態於圖案化藍寶石基板。由掃描式電子顯微鏡發現倒金字塔凹形圖案化藍寶石基板之蝕刻孔穴在氮化鎵磊晶膜表面呈有規律的分佈。相對於藍寶石基板平台處,倒金字塔凹形圖案上方的蝕刻孔穴密度比較少,而凸形圖案化藍寶石基板上則未發現此現象。高解析雙晶繞射與蝕刻孔穴法結果顯示,成長於倒金字塔凹形圖案化藍寶石基板之氮化鎵磊晶膜結晶品質優於凸形圖案化藍寶石基板。倒金字塔凹形圖案化藍寶石基板降低刃差排密度效果比螺旋差排好。倒金字塔凹形圖案化藍寶石基板上成長氮化鎵磊晶膜之螺旋差排密度為~107 cm-2,相對於一般藍寶石基板,刃差排密度則由109 cm-2降到 108 cm-2,相對於凸形圖案化藍寶石基板,光激發光譜積分強度比較強(相對於一般藍寶石基板增加15.7%)。而且隨著刃差排密度降低時,光激發光譜強度有增加趨勢,這現象反應出刃差排可能扮演氮化鎵磊晶膜之非輻射再結合中心。
上述成長於倒金字塔凹形圖案化藍寶石基板上的氮化鎵磊晶膜之材料特性,比較適合作為二次成長氮化鎵磊晶膜的模板。採用無光罩技術製作二氧化矽阻擋層後,二次成長氮化鎵磊晶膜,化學蝕刻法顯示螺旋差排密度為7.3 × 105 cm-2,刃差排為 3.1 × 106 cm-2,相對於直接成長於凹形圖案化藍寶石基板上的氮化鎵磊晶膜,刃差排密度可有效降低~102 cm-2,光激發光譜圖之積分強度則增加40.1%。
其他識別: U0005-0106200714550200
Appears in Collections:材料科學與工程學系

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