以氫化物氣相磊晶法在獨立式氮化鎵基板氮極性面再成長之研究

Abstract

本論文以氫化物氣相磊晶法研究獨立式氮化鎵基板之氮極性面在不同的環境下，磊晶參數對再成長後的表面形貌的影響，以及探討形貌產生的機制。實驗中探討了載氣、溫度、壓力、氨氣流量與磊晶時間等各種環境成長趨勢的變化，並且發現產生之形貌與各晶面的穩定性有關。獨立式氮化鎵基板在氮極性面再成長後，其表面會比在鎵極性面再成長所得到的表面來得粗糙，這是因為氮原子與鎵原子的特性、氮化鎵在鎵極性面與氮極性面晶體結構與氮原子在不同面的擴散係數不同等因素造成的。此外，我們發現氮極性面再成長之磊晶速度不及鎵極性面再成長之磊晶速度的一半。最後，利用二階段成長方式可以有效改善氮化鎵氮極性面再成長後表面粗糙的問題。

In this work, we study the surface morphologies of epitaxial layers obtained from the regrowth on the N-face of freestanding GaN substrates by hydride vapor phase epitaxy (HVPE). The mechanism of the formation of those surface morphologies is also investigated. We discuss the growth trend of changing carrier gas, temperature, pressure, flow rate of ammonia and epitaxial time. We find that the formation of the produced surface can be explained by the stability of crystal facet. It can be observed the surfaces of regrown layers on N-face GaN are rougher than that on Ga-face GaN. The phenomenon can be attributed to the differences of the properties of nitrogen atom and gallium atom, crystal structure and diffusion coefficients of N atoms between Ga-face and N-face GaN. Moreover, we also find that the growth rate of N-face GaN is less than half of that of Ga-face GaN. Finally, we successfully obtain smooth surface of N-face GaN using two-step growth method.