P型氮化鎵歐姆接觸與雷射剝離技術之研究

Abstract

本論文主要探討氮化鎵材料與元件的製程研究，其中包括P型氮化鎵歐姆接觸、准分子雷射蝕刻LED與基板的剝離。在P型歐姆接觸方面，.將鍍在P型氮化鎵表面的Ni/Pd/Au金屬結構在氧氣環境550℃，5分鐘的熱退火處理下，可得到良好的歐姆接觸以及低的特性電阻值1.1×10-4 Ω-cm2 。由SIMS的結果發現，低阻值與氧在熱處理後的金屬結構中含量多寡有關。 在准分子雷射製程方面，我們觀察到氮化鎵所需的臨界分解能量為0.3 J/cm2，此臨界能量與理論數值計算的結果0.29 J/cm2非常相近。利用所得到的蝕刻條件，我們成功地將雷射蝕刻技術用在LED 的製程上。我們亦成功的將氮化鎵薄膜從基板上剝離；而配合金屬黏合（metal bonding），我們亦將藍光LED成功地轉移至Si基板上。其中我們運用了所得到的低阻值結構Ni/Pd/Au 作為P型歐姆接觸，期能使轉移後的藍光LED有更好的操作性能。由PL, x-ray, I-V, and 室溫光譜量測可得知以雷射剝離技術轉移元件至不同的基板上並沒有對元件造成嚴重的破壞。

We study the process techniques of GaN material and GaN-based device including Ohmic contact on p-GaN, Eximer laser etching and laser lift-off of GaN-based LED. For p-GaN Ohmic contact, we developed a new metallization scheme based on Ni/Pd/Au film composition. By deposition of the film on p-type GaN followed by thermal treatment in oxygen ambient at 550℃ for 5 minutes, we obtained good Ohmic characteristic with a specific contact resistivity as low as 1.1×10-4 Ω-cm2. From the SIMS measurement, we found the low specific resistance is related to the content of oxygen within the metallization structure. In Excimer laser processing technique area, we investigated the Excimer laser etching of GaN and obtained the etching rate at fixed laser fluence. From the laser etching data we also obtained a threshold fluence of 0.3 J/cm2 for GaN decomposition. This threshold fluence value is closed to the numerical calculation 0.29 J/cm2. The decomposition of GaN was applied to separate the GaN from the sapphire substrate. We successfully separated GaN films and GaN-based LED from sapphire substrate and transferred on the Si substrate by laser lift-off technique using the KrF laser at laser fluence of 0.8 J/cm2. The Ni/Pd/Au Ohmic contact was deposited on the LED before laser lift-off to assume good performance of the transferred LED. The quality of transferred GaN films and GaN-based LED showed no major change in the quality and device performance as examined by PL, x-ray, I-V, and room-temperature emission characteristic.