以氫化物氣相磊晶法在氮化鎵基板上成長高品質氮化鎵厚膜之研究

Abstract

本論文主要的目的在於成長高品質的獨立式氮化鎵基板，為了成長此基板，我們必須將氮化鎵厚膜長厚以降低其缺陷密度，但又因在藍寶石基板上成長較厚的氮化鎵厚膜容易因熱膨脹不匹配而崩裂，故我們先用雷射剝離法得到獨立式氮化鎵基板，並在其上以同質磊晶的方式將氮化鎵厚膜長厚。在再成長氮化鎵厚膜實驗中，遇到了表面氧化層、表面Pits太多、及厚膜的翹曲等問題，我們使用了濕式蝕刻的方法改善了表面氧化層的問題，使用側向成長的方式降低表面Pits的數目，最後以調變氮化鎵基板長晶層與缺陷密度、及N-Face再成長的方式改善其翹曲程度與應力。最後利用我們的改善方法順利成長出厚度約800um之氮化鎵厚膜，並將缺陷密度降低到6x10-6cm-2。

In this work, the major purpose is growing high quality freestanding GaN substrate. In order to grow this substrate, we have to grow thicker GaN film to reduce its dislocation density. Because growing GaN thick films on sapphire substrates are crack easily by mismatch of thermal expansion. We use freestanding GaN substrate which is separate after laser lift off (LLO), and homoepitaxy to regrowth GaN thick films. In this experiment, we mainly to solve the surface oxide layer, the surface pits, and the bowing of thick films. We use wet etch to solve the problem of surface oxide layer,lateral growth to solve the problem of surface pits. Finally we change epilayer, the difference of dislocation density, and the method of N-Face regrowth to solve the bowing and stress of GaN. In the end, we grow the GaN thick film to 8000um Successfully by our improved method, and reduced the dislocation to 6x10-6cm-2.