石墨烯是碳原子依六角形排列之二維材料,具有高電子遷移率、熱傳導度、機械特性與低片電阻等特性,相較於氧化銦錫,單層石墨烯在波長小於 280 nm下依舊維持>90 %之高穿透率,使其成為應用於深紫外光 LED 之透明導電層最有潛力之材料。本研究首先針對石墨烯/p-Al0.21Ga0.79N 薄膜進行特徵接觸電阻量測,由傳輸線模型計算其特徵接觸電阻為 1.19×10-3 Ω-cm2。具石墨烯電極之 UVC-LED 相較傳統鎳金電極,於注入電流 100 mA 下發光強度提升了 1.3 倍。為提高發光強度,更進一步提出兩種方法製作網狀石墨烯。(1)首先製作直徑約 78 nm 之陽極氧化鋁遮罩,配合氧電漿蝕刻製程製作網狀石墨烯。然而因陽極氧化鋁遮罩與石墨烯存有縫隙造成電漿側蝕嚴重,再加上高阻率之 p-AlGAN 導致無法量測到電致發光光譜。(2)另一方法為沉積薄鎳層,配合高溫製程使鎳層形成奈米粒,此方法製備之網狀石墨烯其電阻率只有 171 Ω-cm,拉曼光譜分析指出 ID/IG=0.66、FWHM2D=37.5 cm-1,部分石墨烯被鎳奈米粒破壞但仍維持二維結構。於注入電流105 mA 下,具鎳奈米粒/石墨烯組成之網狀電極比傳統快速退火後鎳金電極之深紫外光發光二極體強度增加 35 倍。

Graphene is a two-dimensional carbon material with hexagonal crystalline lattice. It has low sheet resistance, high carrier mobility, thermal conductivity, and mechanical properties. Graphene has more than 90% transmittance at wavelengths less than 280 nm, making it a promising candidate as a transparent conductive layer on UVC-LEDs.
To begin, the bulk p-Al0.21Ga0.79N is used to determine the specific contact resistance with graphene. The calculation from the Transmission Line Model will be 1.9×10-3 Ω-cm2. At 100 mA of injection current, the emission intensity of graphene contact is 1.3 times that of traditional Ni/Au contact. To achieve even higher intensity, we propose two methods for making the mesh graphene. (1) Using Anodic Aluminum Oxide (AAO) with 78 nm pore diameter as an O2-plasma etching mask. Nevertheless, inevitable gaps exist between AAO and graphene cause severe plasma side-etching. Because of the high resistivity of p-AlGaN, we were unable to measure the Electroluminescence (EL) spectrum relationship. (2) Depositing nickel film followed by the Rapid Thermal process (RTP) process to creat metal nano-dots on graphene with resistivity of 171 Ω-cm. Raman spectrum reveals its ID/IG=0.66 and FWHM2D=37.5 cm-1 indicating that only parts of graphene are damaged. The EL peak intensity of UVC-LED with nickel nano-dots/graphene hybrid contact is 35 times higher than the sample with traditional Ni/Au contact at 105 mA of injection current.

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