氮化鎵於矽基板上成長時，因晶格不匹配與熱膨脹係數差異引入應力，造成高密度差排缺陷，降低氮化鎵HEMT元件工作效能。本研究提出以石墨烯做為磊晶界面層，提升氮化鎵磊晶品質之方法。石墨烯是二維材料，垂直膜面方向上缺乏懸鍵、與其他物體僅以微弱的凡德瓦力鍵結，利用這項特性減緩基板與氮化鎵間交互作用。研究中採用二種方式於矽基板上成長石墨烯薄膜：(1)鎳薄膜催化類鑽碳之固態碳源合成法 (2)銅薄膜催化甲烷之氣態碳源合成法。方法(1)實驗結果發現，(a)鎳薄膜厚度增加會使生成之石墨烯層數上升，但過薄的鎳會因除潤現象而在高溫下瞬間形成粗糙表面，降低石墨烯品質。(b)石墨烯生成需適當持溫時間，成長時間過短薄膜成長不及而有較多缺陷，持溫過久則因金屬除潤產生粗糙表面導致品質下降。因實驗設備因素，研究中的類鑽碳層強度(硬度)不足，受金屬除潤影響嚴重，無法長時間維持平整表面以成長高品質石墨烯。以此法處理的矽基板實際氮化鎵磊晶結果並不理想，推測是因為石墨烯層數過厚、品質與表面形貌不佳而沒有發揮預期的效果。改以方法(2)成長之石墨烯品質大幅提升，不過在較高的溫度與較長的成長時間下容易生成皺摺、碳粒聚集等表面現象使ID/IG比上升。方法(2)製備的石墨烯樣品具有較佳表面平整度，拉曼光譜I2D/IG比可達2，2D band半高寬39.4 cm-1，為1~2層的石墨烯。

High density of threading dislocations in GaN thin films which generated from a large lattice mismatch and thermal expansion coefficient between GaN and Si substrate degenerate the GaN based HEMTs. It is well known that the graphene exhibits a lot of excellent structural properties such as a 2 dimensional material with a weak van der Waals interaction between neighbor layers. In this study, graphene interlayer is embedded to GaN and Si substrate in order to overcome the lattice mismatch issue.
There are two methods to synthesize graphene interlayer on Si substrate: (1) Graphene prepared by nickel-catalyzed using solid-state carbon source diamond-like carbon (DLC); (2) Graphene prepared by copper-catalyzed using methane precursor. The experimental results indicated that the layer number of graphene increases with increasing thickness of Ni catalyst layer. In addition, the rough surface morphology and poor material quality of graphene can be found due to dewetting behavior when thickness of Ni layer smaller than 5 nm. It is noted that a lot of non-regular concaved hole on the silicon substrate which generated from removing Ni-Si nanorods when graphene processing time more than 30 minutes. Thus, prepared hard DLC layer is a crucial work for further improve the material quality and surface morphology of graphene layer on Si substrate.
Finally, synthesized graphene by methane precursor using Cu catalytic technique was used to prepared high material quality graphene on SiO2/Si substrate. According to Raman spectra, a single-layer graphene with a I2D/IG of 2 and 2DFWHM of 39.4 cm-1 can be achieved in this study. The experimental results also indicated that growth temperature > 1000 oC and/or processing time > 10 minutes may induce carbon clusters and resulting a wrinkles graphene.

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