電漿氮化法製備超薄氮化矽緩衝層於InN奈米柱成長之研究

Study of InN Nanocolumns on Ultra-thin Si_3N_4 Buffer Layer by RF Plasma Nitridation

氮化銦在近年來被量測出具有高載子遷移率（～3500cm^2／V‧s）與約0.65eV之能隙，若是摻雜鋁或鎵元素，則可調整其波長落於0.65－6.2eV之間，因此氮化銦在紅外光區之高效率光電元件中是相當有潛力的材料。然而，由於InN熱裂解溫度較低（＜600°C）且無適合之基板，因此較難製備出高品質之InN薄膜，本研究透過電漿製程對Si基板表面進行氮化後，再以電漿輔助金屬有機分子束磊晶系統在不同基板溫度下進行InN成長，最後利用先進之分析技術探討氮化Si_3N_4與InN／氮化Si_3N_4的微結構、界面探討其物理與化學特性。由實驗結果顯示，當Si_3N_4氮化條件N_2於1.2sccm、氮化時間為60min時，可得到均勻且部分連續之結晶態Si_3N_4薄膜，其厚度約為5nm|XRD與TEM結果顯示，520°C所成長之InN具有相對較佳的結晶品質，並且確認晶體是沿著［0001］方向堆疊成長的六方纖鋅礦結構，由SEM觀察表面形貌發現，InN呈現六方尖錐狀的奈米柱結構並且部分晶柱成長時與基板方向產生偏差|同時透過XPS量測結果亦表明此為接近化學劑量比之InN／Si_3N_4。

InN is a potential material for various devices such as infrared light emitters and high efficiency optoelectronic device because of it is high mobility (~3500 cm^2/v．s) and narrow band gap of 0.65-0.7 eV. Also, Al, Ga-doped InN alloys has band gap of wide range in the 0.65-6.2 eV. However, the InN is difficult to grow high-crystalline-quality InN owing to its low dissociation temperature and the lack of lattice-matched substrates. Therefore, the various properties of InN films have not been fully confirmed. In the study, the Si_xN_y thin films was grown on surface of Si substrate for nitridation by RF-N_2 plasma exposure. And then the InN nanocolumns were prepared on nitrided Si_xN_y/Si(111) via radio-frequency (RF) metal-organic molecular beam epitaxy (MOMBE) with various substrate temperatures. We discussed the effect of various condition on the chemical and structural properties of Si_xN_y ultra-thin film and InN nanocolumns. The surface and interface chemical composition and surface morphology are investigated by using transmission electron microscope (TEM), ellipsometer, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). TEM image indicated that the Si_xN_y film shows relatively surface of smooth with 1 sccm N_2 and 300 W of RF power. Based on X-ray diffraction analysis, highly <0001> -oriented hexagonal InN nanocolumns were grown on the nitride Si(111) substrates. Transmission electron microscopy analysis indicated that the InN nanocolumns were single-phase wurtzite crystals having preferred orientations along the c-axis. SEM images show that the deviation angle of InN nanocolums was measured to evaluate the alignment of arrays. Also, the XPS results indicated that the InN/Si_xN_y were measured at nearly chemical stoichiometric.