近年來，氮化鎵磊晶在矽基板被視為一個重要的技術，此成長法可以降低氮化鎵光電半導體元件的成長。然而氮化鎵成長矽基板上會遇上兩個嚴重的問題，其一熱膨脹係數差異過大，導致降溫時，氮化鎵與矽基板之間容易產生裂縫，另一方面則是晶格常數差異過大，於導致氮化鎵材料中含有大量的缺陷，會大幅降低發光二極體的內部量子效率並影響其輸出功率。在降低缺陷部分，可藉由多次側向磊晶技術 (multi-ELO)、AlGaN/GaN超晶格結構和圖案式基板，尤其是利用多次側向磊晶技術可以大幅度降低缺陷密度，但是此技術需要額外的製程。 因此為了提升氮化鎵半導體在矽基板上的品質，本論文提出一個新穎的成長方法，藉由氮化矽奈米覆蓋層成長多重的錯位島狀結構，自基板附近產生的缺陷會被雙層錯位島狀結構改變行進路徑，進而降低氮化鎵半導體材料中的高密度刃狀差排缺陷和螺旋差排缺陷；更重要的是，此成長法不需要額外的圖案化製程，即可以達到多次側向磊晶技術。本研究針對三種結構探討其結構與光電特性:參考樣品為三層氮化鎵/氮化鋁鎵/氮化鋁堆疊結構，單島狀樣品則在第一層氮化鎵/氮化鋁鎵間插入氮化矽奈米覆蓋層，雙島狀樣品則為在第一和第二層氮化鎵/氮化鋁鎵間插入氮化矽奈米覆蓋層，此三樣品之缺陷密度分別為9.6×109 cm-2 、6×109 cm-2 、2.6×109 cm-2。光激光譜(photoluminescence)實驗顯示，此成長法也可以抑制氮化鎵黃光缺陷訊號。在上述三種結構上成長的藍色發光二極體(LED)亦反映其缺陷密度在光電特性上。LED操作電壓依序降低從(Ref @ 20mA) 3.58 V、3.51 V和3.38 V。相較於參考樣品結構，在20 mA下，具雙島狀緩衝層LED之外部輸出功率和插頭效率分別提升了27%和34.5%。 In recent years, growing GaN on (111) silicon substrates has been regarded as a competitive technique to achieve low-cost optical and power GaN devices. One of the key issues is the 17% lattice constant mismatch between GaN and silicon substrate, resulting a dislocation density as high as 1010 cm-2. Several methods have been proposed to reduce the dislocation density, including multi-epitaxial-lateral-overgrowth (multi-ELO), AlGaN/GaN superlattice and patterned substrate. Although the multi-ELO method could reduce dislocation density significantly, it still needs an extra regrowth process. This paper reports on a new method to reduce threading dislocation density in GaN epilayers grown on (111) silicon substrates by metal-organic vapor phase epitaxy. The method utilizes an in-situ double layer SiNx nano-mask to produce the so-called double island structure with lower dislocation densities without any regrowth procedure. This double island structure can bend and reduce dislocations, which pass through the samples without island structures. Compared to samples without the island structure, there is an improvement in the EPD of the sample grown with the single island structure from 1×1010 cm-2 to 6×109 cm-2. Furthermore, the EPD of the sample with the double island structure can be reduced to 2.6×109 cm-2. This method can also suppress the intensity of yellow luminescence by up to ten times. The operating voltages of LEDs with reference (w/o island structure), single and double island samples were 3.58 V, 3.51 V, and 3.38 V, respectively. Compared to the conventional GaN buffer LED, the output power and wall-plug efficiency are respectively enhanced about 27 % and 34.5 % at an injection current of 20 mA for the LEDs with the double island structures.
