氫化物氣相磊晶法成長氮化鎵奈米線與成長機制探討

Abstract

本實驗利用氫化物氣相磊晶，藉由金屬催化的方式成長氮化鎵奈米線於矽基板上，探討奈米線成長機制、奈米線與矽基板間的關係，並研究磊晶參數對藉由金屬催化成長之氮化鎵形貌的影響。首先將矽基板浸泡於HF以去除其原生氧化層，再利用電子束蒸鍍於不同的矽基板上分別沉積金、鎳及金鎳合金作為催化金屬，最後送入氫化物氣相磊晶機台成長氮化鎵奈米線。 探討奈米線成長機制、奈米線與矽基板間的關係的部分，發現利用鎳作為催化金屬，氮化鎵奈米線藉由VSS機制成長；利用金鎳合金作為催化金屬，氮化鎵奈米線藉由VLS和VSS機制成長。成長過程中，催化金屬－鎳除了會形成合金成為催化顆粒之外，部分鎳也會與矽基板反應生成二矽化鎳。氮化鎵奈米線成長方向與矽基板間存在角度關係，與矽基板夾60o角之奈米線成長方向為[112 ̅0]。 研究磊晶參數對藉由金屬催化成長之氮化鎵形貌的影響部分，實驗中調變溫度、氨氣與氯化氫氣體流量比(Ⅴ/Ⅲ比)和載流氣體總流量等參數，觀察其對成長趨勢的變化，並且發現產生之形貌與金屬催化成長機制有關，磊晶參數之調變改變沉積至矽基板之反應氣體濃度，進而影響金屬催化成長過程中，軸向成長與徑向成長之速度，瞭解磊晶參數之影響趨勢後，我們已經可以穩定地於矽基板上製備氮化鎵奈米線。

We use metal-catalyzed method to grow GaN nanowires on Si substrate by hydride vapor phase epitaxy (HVPE). The buffered hydrofluoric acid is used to etch the native oxide on Si substrates. Au, Ni and Au-Ni alloy films are deposited on the Si substrates using electron beam evaporation. GaN nanowires are then grown on the Si substrate using HVPE. The growth mechanism of nanowires and the epitaxy between nanowires and substrate are investigated. In addition, the growth at different temperatures, Ⅴ/Ⅲ ratios and the amounts of carrier gas flow are discussed.

We find that the Ni-catalyzed nanowires are grown via VSS mechanism. Au-Ni alloy catalyzed nanowires are grown via VLS and VSS mechanisms. There is an angle between the growth front of GaN nanowires and the substrate. The angle between Si substrate and GaN nanowires grown along [112 ̅0] is about 60o. We also discover that a portion of Ni will diffuse into Si substrate and form NiSi2 during the growth process. The orientation and morphology of the nanowires are understood by the axial and radial growth of metal-catalyzed mechanism. We discuss the growth and process parameters, which influence the concentration of the deposited reactants, and the growth mechanisms of the nanowires. We suggest the process parameters for stably producing GaN nanowires on Si substrate.