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    題名: 鎂、鈷摻雜於氮化鎵奈米線之物理特性研究;Physical properties of GaN nanowires with Mg and Co dopants
    作者: 黃秉榮;Ping-Jung Huang
    貢獻者: 物理研究所
    關鍵詞: 奈米線;氮化鎵;nanowires;GaN
    日期: 2008-07-07
    上傳時間: 2009-09-22 10:57:26 (UTC+8)
    出版者: 國立中央大學圖書館
    摘要: 本論文主要研究鎂、鈷摻雜於氮化鎵奈米線的物理特性研 究。首先,單晶的氮化鎵奈米線是利用高溫爐式製程的氣相沉積法在矽基板上成長氮化鎵奈米線。利用掃描式電子顯微鏡、X 光繞射儀、和高解析度穿透式電子顯微鏡可測定出所成長之氮化鎵奈米線為高度方向性的單晶奈米結構。所成長的單晶氮化鎵奈米線經由離子佈植的方式來摻雜鎂、鈷原子,最後在利用高溫爐作熱退火來獲得所要研究的樣品。 在鎂摻雜於氮化鎵奈米線研究部分,鎂離子佈植的條件如 下:60 keV 的佈植能量而佈植劑量為5x1012到5x1014 cm-2。鎂離子佈植之後,我們可以由室溫的螢光光譜看到氮化鎵奈米線的能階邊緣的螢光會隨著熱退火和離子佈植的影響產生紅位移。並且觀察到由鎂所形成的donor-acceptor 對所發出的藍光(~3eV),及離子佈植所造成的缺陷所發的螢光。結構上的觀察到,奈米線相較於薄膜對於缺陷的聚集有比較高度的反應。電性方面,經由鎂離子佈植後的氮化鎵奈米線是呈現p 型半導體的行為。 在鈷摻雜於氮化鎵奈米線研究部分,鈷離子佈植的條件如下:72 keV 的佈植能量而佈植劑量為1x1016到4x1016 cm-2。經由鈷離 子佈植之後,我們可以觀察到鐵磁性的特性且超過室溫的居禮溫度。而經由X 光繞射譜及高解析度穿透式電子顯微鏡分析可以判定,鐵磁性的行為並不是來自於磁性物質的第二相化合物的形成所造成,也由X 光繞射譜確認鈷原子有取代鎵原子。 GaN nanowires were grown by thermal catalytic chemical vapor deposition on Si (1 0 0) substrate with Au catalyst. The GaN nanowires were study by X-ray, TEM, and SEM. The resulting nanowires have the diameters of 60-150 nm and the lengths of 15-20 μm. Structural in the pristine GaN nanowires confirmed the growth direction of high crystalline h-GaN, with the zone axis lying along [001] direction. An energy of 60 keV Mg ions were implanted into the GaN nanowires with various total flux of 5×1012 cm-2 to 5×1014 cm-2. Subsequent thermal annealing treatment was carried out by a furnace at 700°C for 6 min in N2 ambient. Transmission electron microscopy images showed amorphous layer formation and defect accumulation in the higher dose Mg-implanted GaN nanowires after annealing. 300K photoluminescence spectra of the annealed Mg-implanted GaN nanowires exhibited near-band-edge emission (NBE), donor-acceptor pair (DAP) emission, and defect-related yellow luminescence. With increasing dose, the NBE and DAP emissions are red-shifted. Similar phenomena were observed in samples implanted with Ar to produce similar amounts of lattice disorder. The nanowires show a much higher sensitivity to defect accumulation than GaN thin films. The p-type conductivity GaN nanowries were achieved by Mg-ion implantation. GaN nanowires were implanted 72 keV Co+ ions with fluxes of 1x1016 cm-2-4x1016 cm-2. Subsequent thermal annealing treatment was carried out by a furnace at 700°C for 6 min in N2 ambient. Ferromagnetic ordering with Curie temperature above room temperature is recorded for the Co-doped (~ 1-3.85 at%) GaN nanowires. Bound carriers and inhomogeneous doping stabilized in the structural defects introduced by ion beam processing is made responsible for the observed long-range ordering. Our analysis from Co L3,2-shell and Co K-shell x-ray absorption near-edge structure rules out precipitation of Co. A percolative polaron model with carrier mediated coupling of localized magnetic moments is made responsible for the observed ferromagnetic ordering above room temperature.
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