本論文的主旨在探討使用有機金屬化學氣相沉積法選擇區域成長氮化鎵半導體並分析其材料與光學特性。首先，我們在藍寶石基板上研究兩種選擇區域成長氮化鎵的方法，分別是“pendeoepitaxy”以及facet-controlled epitaxial lateral overgrowth (FACELO)”。並且，我們將選擇區域成長法的模式定義為“側向促使模式”與“縱向促使模式”，在此兩種模式中分別具有不同的晶體成長型態與行為並且也影響到差排行進的行為。在FACELO方法中，我們結合以上兩種選擇區域成長模式得到極低的氮化鎵差排密度與較廣的低差排密度區域。此外，我們也利用電子束激發光譜法研究成長於FACELO-氮化鎵的氮化銦鎵/氮化鎵多重量子井的發光特性，從結果中我們可以推論其品質比直接成長於氮化鎵/藍寶石基板之特性還要好，顯示FACELO的成長法成長的低差排密度之氮化鎵基板是對於提升氮化鎵材料元件的效能有極佳的幫助。 在選擇區域成長法成長氮化鎵於圖形化矽基板的方面，我們利用單層高分子塑膠小球陣列鋪於氮化鋁鎵/(111)矽基板表面並以乾式蝕刻法蝕刻成氮化鋁鎵/(111)矽微米柱陣列，再於該氮化鋁鎵/(111)矽上選擇性成長氮化鎵緩衝層。從穿遂式電子顯微鏡的分析結果顯示此氮化鋁鎵種子層上之氮化鎵材料具有極高的差排密度。相較之下，在側向成長氮化鎵的區域之差排密度則顯著降低。並且，在光學特性上，我們也觀察到該氮化鎵材料的電子束光激發光譜強度約高於氮化鎵/(111)矽基板三倍，顯示其較優越的品質。而以拉曼光譜研究材料殘餘應力顯示，氮化鎵成長於氮化鋁鎵/(111)矽基板的殘餘應力約0.373 GPa，而氮化鎵/(111)矽基板的殘餘應力約0.558 GPa，降低了33.2 %。此方法可有效降低以往氮化鎵材料成長在矽基板上產生的龐大差排密度及殘餘應力，顯示氮化鎵材料成長於矽基板極具開發潛力。 此外，我們也研究在V形溝槽化(001)矽基板上成長{1-101}氮化鎵及其氮化銦鎵/氮化鎵多重量子井並探討其成長機制、材料結構及光學特性。觀察其成長過程，可以將其分類成兩階段成長：第一階段為氮化鎵異質成長，與第二階段為氮化鎵同質成長，而在兩種成長階段中均發現無裂線產生。從穿遂式電子顯微鏡的分析結果顯示{1-101}氮化鎵具有較低的差排密度，並且發現該{1-101}氮化鎵晶體的晶格常數已非常接近於應力全釋放之氮化鎵晶格，顯示其材料殘餘應力已被釋放。而在半極性材料特性的分析中，我們成長半極性{1-101}及極性(0001)氮化銦鎵/氮化鎵量子井分別於V形溝槽化(001)矽基板及(111)矽基板，在不同的光激發強度的激發下，發現半極性{1-101}量子井的發光波長藍位移量比極性(0001)量子井較少。並且在時間解析光激發光譜的分析之下，也發現{1-101}量子井的發光生命期比(0001)量子井的發光生命期低了約25倍，發光強度於10 K時提升約兩倍，顯示{1-101}量子井中因為其內建電場降低而使電子電洞波函數空間分佈相疊率增加，進而提升發光強度。 綜合我們的結果，本論文所闡述的是以選擇區域成長法成長低差排密度氮化鎵於藍寶石基板與圖形化矽基板。此低差排密度氮化鎵塊材適合用於發展高效能氮化鎵光電元件，使用圖形化矽基板則有助於降低目前以藍寶石基板成長氮化鎵材料之製造成本。 This dissertation describes selective epitaxial growth techniques of GaN on c-face sapphire and microscale patterned Si substrates. The structural and optical properties of GaN films thus grown, particularly the reduction of dislocation density and residual stress via the selective area epitaxial process and the enhancement of their luminescence properties, are investigated and elucidated. For the selective area epitaxial growth of GaN on c-face sapphire, “pendeoepitaxy” and “facet-controlled epitaxial lateral overgrowth (FACELO)” techniques are employed. Both approaches lead to a significant reduction in dislocation density of the GaN epitaxial layers through a proper arrangement of the lateral enhanced growth mode and vertical enhanced growth mode during the selective area growth. The luminescence properties of InGaN/GaN multiple-quantum-well (MQW) grown on FACELO-GaN are also investigated by cathodoluminescence, and reveal superior efficiency, as compared to the same MQW grown on GaN directly on sapphire. For the selective area growth of GaN on AlGaN/(111)Si, 2 um-thick GaN films without cracks can be achieved by using the substrates with a micropillar array. Transmission electron microscopy (TEM) indicates that dislocation density has been reduced in the lateral growth region, while a large number of dislocations are confined in the heteroepitaxial region. The cathodoluminescence peak intensity of the GaN on AlGaN/(111)Si micropillar array is almost 3 times stronger than that of the GaN on planar AlGaN/(111)Si. It is also found that the residual stress of the GaN grown on AlGaN/(111)Si micropillar array is 0.373 GPa, which is 33.2% lower than that of the GaN grown on planar (111)Si. These results demonstrate the potential of this pillar array template for making low-cost GaN-based devices and free-standing substrates. Semi-polar {1-101}GaN films and InGaN/GaN MQWs have been successfully grown on V-grooved (001)Si substrate. The study on growth evolution reveals that the growth proceeds in two steps, namely heteroepitaxial growth and homoepitaxial growth, sequentially. No crack is found in both two growth stages, implying the low residual stress in the GaN epilayers grown by this technique. This is also confirmed by TEM, which shows that the lattice constant of the {1-101}GaN is very close to that of a fully-relaxed GaN substrate. Power-dependent photoluminescence measurements reveal that {1-101}InGaN/GaN MQW exhibits less wavelength shift than its (0001) counterpart, implying that the internal electric field of semi-polar {1-101}InGaN/GaN MQW is reduced. This is consistent with the results of time-resolved photoluminescence measurements, which show that the PL decay time is significantly shorter for the {1-101}InGaN/GaN MQW (0.44 ns) than the (0001)InGaN/GaN MQW (9.87 ns). Enhanced luminescence efficiency is observed on the {1-101}InGaN/GaN MQW as well. This approach is considered very promising for producing high performance {1-101}GaN-based optical devices on (001)Si. In summary, selective epitaxial growth techniques of GaN on sapphire and microscale patterned Si substrate have been developed and demonstrated in this study. The GaN films grown by these techniques have low dislocation density and residual stress, which manifest their potential in yielding high quality III-nitride semiconductors and devices.
