以二階段氫化物氣相磊晶法製作非極性氮化鎵基板之研究

Abstract

在本論文中，我們成功利用二階段氫化物氣相磊晶成長法成長出110μm厚度的非極性氮化鎵厚膜。我們發現在利用低溫高壓環境成長會形成規則的[1-100]方向的條紋形貌，而此形貌相當類似傳統ELOG成長出來的形貌，後續，我們即利用此形貌做第二階段成長。在第二階段成長中，利用變溫變壓實驗，我們發現隨著溫度變高、壓力變低成長形貌有趨向側向成長與較平坦的趨勢。利用SEM、低溫PL、XRD、拉曼光譜量測，我們發現第一階段成長時間的控制對於後續的側向接平成長與磊晶品質將會產生重要的影響，而第一階段成長時間20分鐘為最佳成長條件。從SEM側面圖我們觀察到二階段成長後產生一些孔洞，這類的孔洞一般只有在利用黃光微影製程的ELOG技術才會產生，在此我們發現一種新的方法來製造孔洞的產生。並且從量測中我們證明孔洞的產生不論對於磊晶品質的改善、應力的釋放皆有相當的影響程度，那也是我們可以成長出100μm以上的厚膜的關鍵因素。

In this research, we obtained the non-polar GaN substrate with a thickness of 110um successfully by two step growth method by hydride vapor phase epitaxy (HVPE). In the step one growth, a-plane GaN were formed triangular stripes along the [10-10] direction under low growth temperature. The morphology of triangular stripes along the [10-10] direction is similar to traditional ELOG GaN. Thus, we use [10-10] stripe GaN to overgrow subsequently for obtaining advantages of ELOG technology. In step two growth, we tried to change pressure and temperature to obtain the best overgrowth condition. Growth direction will become lateral growth under high temperature and low pressure and the morphology of surface will trend to flat. Results measured by SEM, PL, XRD, Raman suggest that the growth time of Step one would dominantly affect crystal quality and subsequent coalescence. The best growth time of step one is twenty minutes. In this work, a new method is presented to produce the voids in a-plane GaN film using two-step growth method without optical lithography process. We also confirm that voids will release a part of stress and stop some basal-plane stacking fault. Existence of voids is a key point to grow 110um non-polar GaN.