關於Ni/Ag 應用於p型氮化鎵的歐姆接觸(ohmic contact)，其電性及光性的表現已經有被廣泛地研究。本篇論文研究主要在於銀裡面添加一點點鋁成為合金去抑制銀在p型氮化鎵表面聚集，提昇歐姆接觸的熱穩定性。 我們發現Ni/Ag歐姆接觸在500 oC熱處理後，氮化鎵表面上有島狀的銀聚集(silver agglomeration)形成。銀聚集(silver agglomeration)的結果導致特徵接觸電阻(specific contact resistance)上升及反射率下降。為了改善此一情況，我們預先將銀和鋁製作成一銀合金靶材來製作電極，其中鋁的組成為10 at.%。接著利用TLM (transmission line method)量測特徵接觸電阻其值為2.25 × 10-2 Ω-cm2，在500 oC長時間下發現銀鋁合金的特徵接觸電阻較純銀穩定。另外用四眼探針法(four-point probe method)量測片電阻(sheet resistance)亦發現銀鋁合金較純銀穩定，在400 oC ~ 700 oC的溫度條件下。而且在500 oC下為87 % @ 460nm之高反射率。因此我們提出Ni/Ag(Al)的結構可以有效抑制銀的聚集，提升歐姆接觸的熱穩定性，並且同時擁有高反射率的特性。 The thermal stability of Ni/Ag and Ni/Ag(Al) p-GaN contacts in relation to their electrical and optical properties was investigated. Ag agglomeration was found to occur at Ni/Ag to p-GaN contacts after annealing at 500 oC. This Ag agglomeration led to the poor thermal stability showed by the Ni/Ag contacts in relation to the reflectivity and electrical properties. However, after alloying with 10 at.% Al, the Ni/Ag(Al) p-GaN contacts were found to be free of Ag agglomeration thereby greatly enhancing the thermal stability. The values of the specific contact resistance and relative reflectance of the Ni/Ag(Al)samples was 2.25×10-2 Ω-cm2 and > 87%, at 460 nm after annealing at up to 600 oC .
