本篇論文中，我們利用硫化的方法對P型氮化鎵進行表面處理，並且以電子槍蒸鍍機蒸鍍鎳/金薄金屬於P型氮化鎵上，金屬膜厚度為25Å/25 Å。接著於空氣的環境下，將試片以500℃進行熱處理，結果可以得到良好的歐姆接觸特性，以及低特徵電阻值達10-6Ωcm2這個級數。 由於傳統金屬電極有遮光，與電流無法均勻擴散等缺點，我們希望以銦錫氧化膜的高穿透率，以及高導電性等特性來克服傳統電極的缺點。然而因為銦錫氧化膜為N型半導體材料，所以與P型氮化鎵接觸時有P-N接面的問題，我們便設計新電極結構來改善上述問題。另外我們也以穿透率光譜觀察薄膜在發光中心波長為470nm的穿透率，鎳/金薄金屬在含氧環境下熱處理後，穿透率可達90﹪以上；而新結構的電極在熱處理後，穿透率約在80﹪。 我們除了電流-電壓特性的量測外，也利用原子力顯微鏡觀察硫化處理對P型氮化鎵表面粗糙度的影響，以及薄金屬在熱處理前後的分佈情形。實驗結果發現經過硫化處理的氮化鎵試片表面粗糙度明顯降低；蒸鍍鎳/金薄金屬於硫化處理之P型氮化鎵後也同樣有較佳之平整度；試片進一步的熱處理，發現經過硫化處理之P型氮化鎵表面的薄金屬呈現一個較平整且連續的分佈情形。 另外在實驗過程中，我們發現試片在熱處理時，有水汽的加入不會導致鎳/金金屬膜與P型氮化鎵的接觸特性變差，但是有水汽加入熱處理製程的試片，其表面的金屬分佈呈現一個較不均勻的結果，並且進而影響元件特性。 Low resistance and reliable ohmic contacts to both n- and p-type GaN:Ohmic contacts with low contact resistance are essential in improved GaN based on LEDs. For n-type GaN, ohmic contacts with low contact resistance have been achieved by several research groups, including our group . On the other hand, the contact resistance for ohmic contact to p-GaN was too high to need the requirement for GaN-based optical devices. According to our previous studies for (NH4)2Sx-treated Si- and Mg- doped GaN surface, we found that the original native oxide on the GaN surface was effectively removed by the (NH4)2Sx solution and a specific contact resistance of 5.0×10-5Ωcm2 for the Ti/Al nonalloyed ohmic contacts to (NH4)2Sx -treated n-type GaN can be obtained. Therefore, in this plan, high performance of ohmic contact with the (NH4)2Sx-treated p-GaN surface will be investigated. In addition, conventional opaque metals were used as p-type electrode contacted with semiconductors in electronic and optoelectronic device. However, the resultant devices suffer from very low external quantum efficiency due to the great blocking and shadowing of incident or radiative lights by opaque electrodes. To improve the external quantum efficiency, the method to avoid this so called current crowding problem, thereby obtaining high efficiency and uniform light emission from the device is to reduce the specific contact resistance of the very thin metal contact to p-GaN.
