近年來，第三代寬能隙半導體材料氮化鎵被廣泛應用於高頻及高功率元件，然而高功率操作下元件廢熱堆積，會使元件特性衰退，傳統金屬電極也有熱退化問題。本研究在氮化鎵高電子遷移率電晶體(GaN HEMT)基板上使用金屬摻雜調變石墨烯功函數，使其能在GaN上形成歐姆與蕭特基接觸，製備石墨烯電極，其高熱傳導特性能輔助散熱，提高元件熱穩定性。藉由使用氮摻雜超奈米晶鑽石薄膜(N-UNCD)作為固態碳源，配合鎳金屬催化層之熱處理轉換技術製備石墨烯薄膜。研究初期通過調整N-UNCD成長的預熱溫度、加入偏壓以及調整氮氣流量提高成核密度並降低石墨烯的電阻率，成功在氮化鎵基板上成長出均勻度高，電阻率的10 Ω-cm的連續石墨烯薄膜。
通過金屬摻雜方式在GaN HEMTs基板上製作石墨烯歐姆與蕭特基接觸，經變溫I-V量測，石墨烯歐姆接觸呈現正溫度係數，為過渡金屬特性；石墨烯蕭特基接觸在配合類鑽碳膜作為鈍化層後具有0.95 eV的蕭特基能障與1.36的理想因子。在變溫I-V量測中與傳統金屬相反，蕭特基能障隨溫度上升而增加，理想因子隨溫度上升而下降，適合在高溫操作下使用。後續使用金屬摻雜石墨烯電極結構應用在氮化鎵高電子遷移率電晶體，石墨烯電極具有較傳統金屬電極更高的飽和電流，適合高功率應用。通過調變閘極偏壓能夠觀察到飽和電流變化，能調變空乏區寬度，具控制能力；然而元件無法隨閘極逆偏壓的增加而截止。在變溫Ids-Vds量測中，石墨烯電極在320 oC下較室溫時僅有39%衰退，而傳統金屬電極則有51%衰退。在350 oC環境進行熱穩定性量測中，傳統金屬電極在2小時後有明顯衰退現象，電阻值也有所上升，而石墨烯電極則維持穩定，顯示石墨烯電極具有較佳的熱穩定性，適合應用於高功率操作。

In recent years, GaN, a third-generation wide-bandgap semiconductor material GaN has been widely used in high-frequency and high-power devices. However, the accumulation of waste heat in high-power operation causes characteristics degradation in devices and traditional metal electrode. In this study, graphene electrodes were prepared on GaN HEMTs by metal doping method, which could modulate the work function of graphene to fabricate graphene ohmic and Schottky contacts on GaN. With high thermal conductivity, graphene electrode improves both heat dissipation and thermal stability. Multi layer graphene (MLG) is prepared by using ultrananocrystalline diamond(N-UNCD) as solid carbon source with nickel metal catalyst technique. By adjusting the preheating temperature, adding bias pressure and adjusting the nitrogen flow rate in N-UNCD growth to increase its nucleation density and reduce the electrical resistivity of graphene, a continuous graphene film with high uniformity and 10 Ω-cm electrical resistivity was successfully grown on the GaN HEMTs.
In I-V-T measurement, graphene ohmic contact exhibits transition metal property with a positive temperature coefficient (PTC). Graphene Schottky contact has a Schottky barrier height of 0.95 eV and an ideality factor of 1.36 after diamond like carbon (DLC) film is grown as passivation layer. In contrast to traditional metal electrode, the Schottky barrier height of graphene electrode increases and its ideality factor decreases with increasing temperature, making them suitable for high temperature operation. Next, graphene electrode is grown on GaN HEMTs, the saturation current variation can be observed by adjusting the gate bias voltage, meaning that the width of the depletion region can be adjusted and the controllability of gate. In temperature change Ids-Vds measurement from room temperature to 320oC, graphene electrode decays only 39%, while the conventional metal electrode decays by 51%. In the thermal stability measurement at 350 oC, traditional metal electrodes showed significant degradation after 2 hours and the resistance value also increased, while graphene electrode remained stable, indicating that the graphene electrode has better thermal stability, suitable for high power operation.

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