獨立式氮化鎵厚膜化學機械研磨與同質磊晶之研究

Abstract

氮化鎵為現今重要的半導體材料之一，不論是在光電或是電子元件。本論文是針對利用氫化物氣相磊晶法所成長的氮化鎵厚膜，進行化學機械研磨製程，藉此製作可磊晶之氮化鎵基板。 我們利用化學機械研磨製程技術，將氮化鎵厚膜高低差將近50微米，平坦化至1奈米以下。研磨製程除了將氮化鎵厚膜表面的粗糙度降低，研磨過程中伴隨的是損害層的產生。損害層會造成後續磊晶的品質下降，而過去損害層的觀察是透過電子顯微鏡，本研究使用光激發螢光觀察，將主訊號強度與yellow band強度做比值的計算，我們稱為”PY值”，當PY值之回升，代表損害層去除。而因為化學研磨液與氮化鎵的反應，造成氮化鎵表面的氧化層生成，透過濕式蝕刻的方式去除，最後產出可以同質磊晶的氮化鎵基板。我們選擇近紫外光與藍光發光二極體成長在我們所研磨之後的氮化鎵基板，近紫外光的波長設定在380奈米，藍光則是455奈米，兩種發光二極體Efficiency Droop皆為約16%。透過此元件的表現，來驗證我們所研磨的氮化鎵基板。而因為氮化鎵極性與獨立式氮化鎵基板的關係，我們可以成長不同極性面的氮化鎵，成功的成長出{11-20}與氮極性面的氮化鎵。

In the recent years, GaN is an important material of semiconductor for optical and electric devices. In this work, we polsied free-standing GaN thick film grown by hydride vapour phase epitaxy using chemical mechanical polishing technique to manufacture GaN substrate. We polished free-standing GaN thick film which difference of height was 50 μm using chemical mechanical polishing technique. After polising, the surface roughess reduced to 1 nm. The polishing process reducing surface roughness but also induced damage layer on the surface of GaN substrate. The damage layer on the surface caused decreasing quality of epilayer grown on GaN substrate. In the past, damage layer was observed by TEM. In this study, we used photoluminescence technique to observe it. The ratio of intensity of main peak to intensity of yellow band was named as PY vaule. When PY value was increasing, it mean that damage layer was removed. Beside, the oxside layer on GaN surface was form because of the reaction bwtween polishing slurry and GaN. The oxside layer was removed by wet etching. Finally, epi-ready GaN substrate was manufactured. In order to verify the manufactured GaN substrate, we grew UV- and blue-LED on it. The wavelength of UV- and blue-LED was 380 nm and 455 nm, repectively. We could vertify the quality of the GaN substrate by the performances of LEDs. Because of polarity and free-standing GaN, we can grow various GaN faces. We successfully grew a-plane GaN and N-face GaN.