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標題: | 規則排列氮化鎵奈米柱發光二極體陣列的生長與元件製程 Growth and Device Process of Regularly-patterned GaN Nanorod Light-emitting Diode Arrays |
作者: | Charng-Gan Tu 杜長耕 |
指導教授: | 楊志忠 |
關鍵字: | 有機金屬氣相沉積,流量調變磊晶法,氮化鎵奈米柱,核殼結構奈米柱發光二極體,多截奈米柱, metal-organic chemical vapor deposition,pulsed growth mode,GaN nanorods,core-shell nanorod light-emitting diodes,multi-section nanorod, |
出版年 : | 2015 |
學位: | 博士 |
摘要: | 在本論文中,首先我們報告利用有機金屬氣相沉積法於氮化鎵/藍寶石基板上成長高晶體品質氮化鎵奈米柱。藉由奈米壓印技術及選區磊晶得到結構一致且規則排列氮化鎵奈米柱陣列。並可於朝c軸成長之氮化鎵奈米柱陣列之頂端c晶面、側壁m 晶面或半極性晶面上成長氮化銦鎵/氮化鎵量子井結構,其中沿c晶面與半極性晶面成長速率為最快及最慢。於n 型氮化鎵核狀結構上成長量子井及p型殼狀結構便可得到核殼結構之奈米柱發光二極體陣列。接下來我們成長並製作發光來自側壁非極性量子井的奈米柱發光二極體陣列。藉由奈米柱陣列的頂端成長無摻雜的金字塔型結構及奈米柱外包覆氧化鋅鎵透明電層可幫助注入電流有效地導通並激發奈米柱側壁的量子井。奈米柱發光二極體陣列的電特性與平面結構之c及m晶面發光二極體類似。由於側壁量子井之寬度與銦含量分布不均勻,造成奈米柱發光二極體陣列隨著不同電流注入發光波長藍移。藉由逆偏光致激發螢光實驗可以確認奈米柱發光二極體之光源自於非極性量子井。隨後,我們成長基於流量調變磊晶法之多截結構氮化鎵奈米柱陣列,於成長過程中,下降鎵的供給時間可使鎵催化粒子縮小並使氮化鎵奈米柱截面大小縮減。由掃瞄電子顯微及穿透電子顯微影像,我們觀察到介於兩段成長週期間的線標記,其主要由成長過程中形成的富鎵層所組成。藉由分析線型標記,可以得到多截結構氮化鎵奈米柱形貌隨著成長週期的演變過程。多截結構奈米柱形貌的改變,主要由奈米柱頂端鎵催化粒子的大小及其覆蓋斜面的範圍所控制。我們比較於單截、雙截及三截奈米柱上成長之氮化鎵/氮化銦鎵量子井結構,多截奈米柱可達到較寬的側壁發光頻寬。最後,我們成長並製作雙截核殼結構氮化銦鎵/氮化鎵量子井奈米柱發光二極體陣列,並藉由陰極射線致發螢光、光致發螢光、電致發螢光比較其與相同高度之單截奈米柱發光二極體之發光特性。因為雙截結構奈米柱與鄰近奈米柱之間距較大,其單位面積銦原子供給量較高,且雙截結構應力鬆弛效果較強,造成其量子井有較高的銦含量,使得雙截核殼結構奈米柱發光二極體有較單截發光波長較長且頻譜寬度較廣之特性。 In this dissertation, we first demonstrate the growth of high-quality GaN nanorods (NRs) by metal-organic chemical vapor deposition (MOCVD) on patterned GaN/sapphire growth template. With nano-imprint lithography technique and selective area epitaxy, we can obtain regularly-patterned GaN NR array. The growth of GaN NR array starts with a hole-filling process, followed by NR growth with pulsed growth mode through switching group III supply (TMGa) and group V supply (NH3) on and off alternatively. Regularly-patterned GaN NR array of uniform geometry are formed. InGaN/GaN quantum wells (QWs) can be deposited on the c-plane top faces, m-plane sidewalls, and {1-101}-plane slant facets on c-oriented NR array with highest (lowest) growth rate in the c-plane ({1-101}-plane). After regrowth of p-GaN on NR array with n-cores and QWs deposition, an NR light-emitting diode (LED) array can be implemented. Then, we demonstrate the growth and process of a regularly-patterned NR-LED array with its emission from sidewall non-polar QWs. A pyramidal un-doped GaN structure is intentionally formed at the NR top for minimizing the current flow through this portion of the NR such that the injection current can be effectively guided to the sidewall m-plane InGaN/GaN QWs for emission excitation by a conformal transparent conductor (GaZnO). The injected current density at a given applied voltage of the NR-LED device is similar tothat of a planar c-plane or m-plane LED. The blue-shift trend of NR LED output spectrum with increasing injection current is caused by the non-uniform distributions of QW width and indium content along the height on a sidewall. The photoluminescence (PL) spectral shift under reversed bias confirms that the emission of the fabricated NR-LED originates from non-polar QWs. Next, the growth of regularly-patterned multi-section GaN NR arrays based on a pulsed growth technique is demonstrated. Such an NR with multiple sections of different cross-sectional sizes is formed by tapering a uniform cross section to another through the decrease of Ga supply duration stepwise for reducing the size of the catalytic Ga droplet. Line-markers are observed in either a scanning electron microscopy (SEM) or a transmission electron microscopy (TEM) image of an NR for illustrating the boundaries between two successive growth cycles in pulsed growth. A line-marker corresponds to a thin Ga-rich layer formed at the beginning of GaN precipitation of a pulsed-growth cycle. By analysing the geometry variation of the line-markers, the morphology evolution in the growth of a multi-section NR, including a tapering process, can be traced. Such a morphology variation is controlled by the size of the catalytic Ga droplet and its coverage range on the slant facets at the top of an NR. The comparison of emission spectrum between single-, two-, and three-section GaN NRs with sidewall InGaN/GaN quantum wells indicates that a multi-section NR can lead to a significantly broader sidewall emission spectrum. Finally, we demonstrate the growth of a two-section, core-shell, InGaN/GaN QWs NRLED device. A two-section n-GaN NR is grown through a tapering process for forming two uniform NR sections of different cross-sectional sizes. The cathodoluminescence (CL), PL, and electroluminescence (EL) characterization results of the two-section NR structure are compared with those of a single-section NR sample, which is prepared under the similar condition to that for the first uniform NR section of the two-section sample. All the CL, PL, and EL spectra of the two-section sample are red-shifted from those of the single-section sample. Also, the emitted spectral widths of the two-section sample become significantly larger than their counterparts of the single-section sample. Such variations are attributed to the higher indium incorporation in the sidewall QWs of the two-section sample due to the stronger strain relaxation in an NR section of a smaller cross-sectional size and the more constituent atom supply from the larger gap volume between neighboring NRs. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/54097 |
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