矽鍺半導體異質界面奈米線的成長與分析

Growth and Analysis of SiGe Heterojunction Nanowires

李欣諭(Hsin-Yu Lee)

指導教授 ： 溫政驗

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201800294

摘要

矽鍺異質界面可以提供優良的電學及光學性質，能夠被應用於高效率的半導體元件中，這其中仰賴的是無缺陷且分明的界面，然而大面積層狀的異質界面容易因晶格常數差異產生缺陷，因此在奈米線中製造異質界面是解決方法之一。最為常見的奈米線成長機制是氣液固相成長機制，利用此機制製造矽鍺異質界面奈米線的實驗也不在少數，但是液態催化劑的高固溶度使得矽鍺之間的轉換十分模糊，無法產生分明的界面。本研究基於調整催化劑中的半導體材料成分的想法，提供了兩種方法製造矽鍺異質界面奈米線。一種是以氣固固相成長機制成長奈米線，固態催化劑的低固溶度讓半導體材料可以很快地切換；另一種是將矽鍺合金奈米線在高溫下氧化，利用矽與鍺氧化的差異性，與高溫下的擴散性，使得催化劑內的鍺濃度在析出前不斷提昇，達飽和後便能直接析出異質材料，形成具有成分差異的異質界面結構，並在多面向的嚴謹觀察後，提出此異質結構形成的機制。

關鍵字

矽 ； 鍺 ； 異質界面 ； 氣相固相固相機制 ； 氧化 ； 奈米線

並列摘要

Group IV semiconductor heterojunction nanowires have a wide range of potential applications in transistors and thermoelectric devices. For these applications, perfection of the interfacial structure at the heterojunctions is essential for the ideal device performance. Heterojunction nanowires are usually fabricated by switching the gas precursors during the vapor-liquid-solid (VLS) growth. However, the large solubility of Si and Ge in the eutectic liquid catalyst inevitable restricts the formation of abrupt interfaces. The key to the formation of an abrupt interface is making a sharp concentration change of the semiconductor in the catalysts before precipitation of the second phase. Here we show that both vapor-solid-solid (VSS) growth method and oxidizing SiGe alloy nanowires can produce an abrupt interface. The solid catalyst in the VSS growth has low semiconductor solubility, so that the compositional switch for the growth of heterojunctions can be prompt. Alternatively, a heterojunction interface can be formed in SixGe1-x (x=0.06) nanowires by thermal oxidation at 700°C in air. During the oxidation, the composition in the AuSiGe eutectic liquid on nanowire tips is altered – Si is selectively oxidized on the surface of the eutectic liquid and the Ge/Si ratio in the eutectic liquid is changed. The subsequently precipitated SiGe alloy at the liquid/solid interface has a higher Ge/Si ratio, and a compositionally abrupt interface is therefore produced in the nanowires. The formation mechanism of the heterojunction is proposed based on the transmission electron microscopy analysis.

並列關鍵字

silicon ； germanium ； heterojunction ； vapor-solid-solid mechanism ； oxidation ； nanowires

參考文獻

1. K. Terashima, M. Tajima, et al., Near-band-gap photoluminescence of Si1-xGex alloys grown on Si(100) by molecular-beam epitaxy, Appl. Phys. Lett. 57, 1925-1927 (1990).

2. J. C. Sturm, H. Manoharan, et al., Well-resolved band-edge photoluminescence of excitons confined in strained Si1-xGex quantum-wells, Phys. Rev. Lett. 66, 1362-1365 (1991).

3. L. Esaki, New phenomenon in narrow germanium para-normal-junctions, Phys. Rev. 109, 603-604 (1958).

4. Z. Alferov, Double heterostructure lasers: Early days and future perspectives, IEEE J. Sel. Topics Quantum Electron. 6, 832-840 (2000).

5. A. Wolfsteller, N. Geyer, et al., Comparison of the top-down and bottom-up approach to fabricate nanowire-based silicon/germanium heterostructures, Thin Solid Films 518, 2555-2561 (2010).