在紫外光 (UV) 覆晶式發光二極體之光反射式歐姆電極應用中，純Al之紫外光反射率最為優秀，但純Al與p-GaN間因功函數差異，不能形成歐姆接觸，因此本研究利用高功函數的Ni及Pd作為Al與p-GaN間的接觸層來提升界面導電特性。本論文以雙電子槍蒸鍍系統製備p-GaN的紫外光反射式歐姆電極Ni (1 nm)/Al (160 nm)、Ni (2.5 nm)/Al (160 nm)、Ni (5 nm)/Al (160 nm)、Ni (8 nm)/Al (160 nm)及Al48Ni52 (60 nm)/Al (100 nm)；Pd (2.5 nm)/Al (160 nm)、Pd (5 nm)/Al (160 nm)及Al25Pd75 (9 nm)/Al (160 nm) 等八組試片，研究不同Ni與Pd接觸層厚度及不同退火溫度對於Ni/Al及Pd/Al紫外光反射式歐姆電極光電特性的影響，探討內容主要為歐姆電極的光反射率、金屬薄膜片電阻與特徵接觸電阻。實驗結果顯示，隨著接觸層Pd或Ni厚度的增加，UV光反射率下降；隨著退火溫度上升，部分的Al可以擴散到界面使光反射率增加，但是造成電性劣化。固定退火400 ℃時，在相同接觸層材料中，接觸層越厚，其特徵接觸電阻越低；而在相同接觸層厚度下，Pd/Al的特徵接觸電阻又比Ni/Al低。在Ni-Al系統中，可形成歐姆接觸退火的最高溫度為400 ℃，而在Pd-Al系統中，最高溫度為500 ℃。綜合考量退火溫度、UV光反射率與特徵接觸電阻，Pd (5 nm)/Al (160 nm) 快速退火400 ℃後可得最低特徵接觸電阻 3×10-3 Ω-cm2，光反射率約58%-63% (270 nm-350 nm)；Al25Pd75 (9 nm)/Al (160 nm) 退火500 ℃後可得最低特徵接觸電阻2×10-2 Ω-cm2，光反射率約58%-63% (270 nm-350 nm)；而Ni (5 nm)/Al (160 nm) 快速退火400 ℃後可得特徵接觸電阻3×10-1 Ω-cm2，但光反射率約70% (270 nm-350 nm)。

The ultraviolet light reflectivity of Al is the most excellent in the applications of flip-chip ultraviolet reflective light-emitting diodes (UV LED). However, because of low work function of Al, it can not form ohmic contact with p-GaN. Therefore, contact metals such as Ni or Pd is needed to obtain the ohmic contact with p-GaN.
Ni (1 nm)/Al (160 nm)、Ni (2.5 nm)/Al (160 nm)、Ni (5 nm)/Al (160 nm)、Ni (8 nm)/Al (160 nm), Al48Ni52 (60 nm)/Al (100 nm), Pd (2.5 nm)/Al (160 nm)、Pd (5 nm)/Al (160 nm) and Al25Pd75 (9 nm)/Al (160 nm) were prepared to study the effects of Ni or Pd contact layer thickness and annealing temperature on the photoelectric properties of optical reflective ohmic contacts.
In this study, optical reflectivity and contact resistivity of Ni/Al and Pd/Al ohmic contacts to p-GaN were investigated. In contrast to Ni/Al samples, Pd/Al contacts retained their linear Current-Voltage curve after rapid thermal annealing at 500 °C in argon ambient. According to the results of the study, it is suggested that the UV reflectivity decreases with the increase of the thickness of Pd or Ni contact layer. As the annealing temperature increases, Al diffuses to the interface between metal and p-GaN to increase the optical reflectivity, but causes the electrical deterioration. At the same contact layer thickness, the specific contact resistance of Pd/Al is lower than Ni/Al. In Ni-Al system, the maximum annealing temperature for ohmic contact can be 400 ° C, while in Pd-Al system, the maximum annealing temperature is 500 ° C. After 400 ° C rapid thermal annealing, Pd (5 nm) / Al (160 nm) could obtain the lowest specific contact resistance of 3 × 10-3 Ω-cm2 with optical reflectivity about 58%-63% (270 nm-350 nm), and Ni (5 nm)/Al (160 nm) obtains specific contact resistance of 3 × 10-1 Ω-cm2 with optical reflectivity about 70% (270 nm-350 nm). After 500 ° C rapid thermal annealing, Al25Pd75 (9 nm)/Al (160 nm) obtains the specific contact resistance of 2 × 10-2 Ω-cm2 with optical reflectivity about 58%-63% (270 nm-350 nm).

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