本研究是利用電子槍真空系統，蒸鍍上一層厚度約為 1 nm 的金(Au)薄膜於SI GaAs (111)B 的基板上，再送進超高真空分子束磊晶系統成長砷化鎵奈米線。運用常規成長奈米線的氣液固機制(VLS)，將試片加熱至600 ℃去除砷化鎵氧化層，並且使金薄膜凝聚形成奈米級尺寸之金屬液滴，以作為VLS機制中的金屬觸媒，接著降溫至540℃成長奈米線。透過掃瞄式電子顯微鏡(FESEM)觀察中我們發現，當改變不同的實驗參數如成長溫度、成長時間及Ga、As的束流(flux)時，可以得到奈米線的形貌與實驗參數的調變具有一定依存關係之初步結果。更進一步地，我們運用這些參數調整創造了”變溫式分段成長法”，成功的組建出具備核殼(Core-shell)結構的砷化鎵奈米線。
藉由掃描式電子顯微鏡來觀察奈米線的形貌變化中，我們發現在固定As束流的情況下，奈米線的管徑隨Ga束流的增加而增加；而在固定Ga束流的情況下，奈米線的長度隨As束流的增加而增長。另外再利用穿透式電子顯微鏡的分析，我們可以得出隨著生長速率提昇，奈米線的缺陷會顯著增加，造成奈米線的磊晶品質下降之結果。

In this work, GaAs nanowires were grown on the GaAs (111)B substrate by molecular beam epitaxy (MBE). First, Au film with a thickness of 1 nm was deposited onto the GaAs (111)B substrate through e-gun evaporation to form metal seeds for further VLS growth of GaAs nanowires. After Au film deposition, the sample was inserted into MBE chamber, heated up to the desired temperature of 600℃ in order to remove the oxide layer and to form droplets of eutectic Au-Ga liquid alloy. After annealing, GaAs nanowires were grown at a substrate temperature of 540 ℃. With various growth parameters, i.e. time, temperature and source BEP, the morphologies of nanowires were changed. Hence, the GaAs nanowire with core- shell structure could be obtained by adjusting different parameters such as Ga, As fluxes and growth temperature.
The nanowires were systematically investigated using different instruments. Scanning electron microscope (SEM) demonstrates different morphologies of nanowires. The diameter of nanowires is increasing with increasing Ga flux under a constant As flux, while the axial growth rate is increasing with increasing As flux under a constant Ga flux. From the observation of Transmission electron microscopy (TEM), a great deal of defects, e.g. stacking faults and twins, were found in the nanowires with increasing growth rate. Thus, this growth condition mentioned above resulted in a worse quality of nanowires.

第六章 參考文獻

1. Iijima, S., HELICAL MICROTUBULES OF GRAPHITIC CARBON. Nature, 1991. 354(6348): p. 56-58.
2. Qian, F., et al., Core/multishell nanowire heterostructures as multicolor, high-efficiency light-emitting diodes. Nano Letters, 2005. 5(11): p. 2287-2291.
3. Law, M., et al., Photochemical sensing of NO2 with SnO2 nanoribbon nanosensors at room temperature. Angewandte Chemie-International Edition, 2002. 41(13): p. 2405-2408.
4. Cui, Y., et al., High performance silicon nanowire field effect transistors. Nano Letters, 2003. 3(2): p. 149-152.
5. Kayes, B.M., H.A. Atwater, and N.S. Lewis, Comparison of the device physics principles of planar and radial p-n junction nanorod solar cells. Journal of Applied Physics, 2005. 97(11).
6. Landes, C.F., et al., Some properties of spherical and rod-shaped semiconductor and metal nanocrystals. Pure and Applied Chemistry, 2002. 74(9): p. 1675-1692.
7. Mohamed, M.B., C. Burda, and M.A. El-Sayed, Shape dependent ultrafast relaxation dynamics of CdSe nanocrystals: Nanorods vs nanodots. Nano Letters, 2001. 1(11): p. 589-593.
8. Schubert, E.F., Quantum mechanics and quantum structures 2003.
9. 林群傑, 曾., 材料會訊, 92年十二月. 第十卷(第四期).
10. Tseng, T.Y., (Ba,Sr)TiO3 thin films: Preparation, properties and reliability. Ferroelectrics, 1999. 232(1-4): p. 881-893.
11. Liu, C.Y., H.T. Lue, and T.Y. Tseng, Effects of nitridation of silicon and repeated spike heating on the electrical properties of SrTiO3 gate dielectrics. Applied Physics Letters, 2002. 81(23): p. 4416-4418.
12. R. Victor Jones, R.L.W.; Available from: http://people.seas.harvard.edu/~jones/es154/lectures/lecture_2/covalent_bond/diam_struct_1.jpg.
13. Zardo, I., et al., Raman spectroscopy of wurtzite and zinc-blende GaAs nanowires: Polarization dependence, selection rules, and strain effects. Physical Review B, 2009. 80(24): p. 245324.
14. McMahon, M.I. and R.J. Nelmes, Observation of a wurtzite form of gallium arsenide. Physical Review Letters, 2005. 95(21).
15. Jones, R.V.; Available from: http://people.seas.harvard.edu/~jones/ap216/images/bandgap_engineering/bandgap_engineering.html.
16. Available from: http://www.ioffe.ru/SVA/NSM/Semicond/GaAs/basic.html.
17. Xia, Y.N., et al., One-dimensional nanostructures: Synthesis, characterization, and applications. Advanced Materials, 2003. 15(5): p. 353-389.
18. Wagner, R.S. and W.C. Ellis, VAPOR-LIQUID-SOLID MECHANISM OF SINGLE CRYSTAL GROWTH ( NEW METHOD GROWTH CATALYSIS FROM IMPURITY WHISKER EPITAXIAL + LARGE CRYSTALS SI E ). Applied Physics Letters, 1964. 4(5): p. 89-&.
19. PEIDONG YANG, Y.W., and RONG FAN, INORGANIC SEMICONDUCTOR NANOWIRES. International Journal of Nanoscience, 2002. 1(1): p. 1-39.
20. Tchernycheva, M., et al., Temperature conditions for GaAs nanowire formation by Au-assisted molecular beam epitaxy. Nanotechnology, 2006. 17(16): p. 4025-4030.
21. Plante, M.C. and R.R. LaPierre, Control of GaAs nanowire morphology and crystal structure. Nanotechnology, 2008. 19(49).
22. Shtrikman, H., et al., Stacking-Faults-Free Zinc Blende GaAs Nanowires. Nano Letters, 2009. 9(1): p. 215-219.
23. Morral, A.F.I., et al., Nucleation mechanism of gallium-assisted molecular beam epitaxy growth of gallium arsenide nanowires. Applied Physics Letters, 2008. 92(6).
24. Colombo, C., et al., Ga-assisted catalyst-free growth mechanism of GaAs nanowires by molecular beam epitaxy. Physical Review B, 2008. 77(15): p. 155326.
25. Dubrovskii, V.G., et al., Diffusion-induced growth of GaAs nanowhiskers during molecular beam epitaxy: Theory and experiment. Physical Review B, 2005. 71(20).
26. Czaban, J.A., D.A. Thompson, and R.R. LaPierre, GaAs Core-Shell Nanowires for Photovoltaic Applications. Nano Letters, 2009. 9(1): p. 148-154.
27. Colombo, C., et al., Gallium arsenide p-i-n radial structures for photovoltaic applications. Applied Physics Letters, 2009. 94(17).
28. Chatillon, C., F. Hodaj, and A. Pisch, Thermodynamics of GaAs nanowire MBE growth with gold droplets. Journal of Crystal Growth, 2009. 311(14): p. 3598-3608.
29. Arthur, J.R., J. Appl. Phys., 1968. 39: p. 4032.
30. Hill, M., Molecular Beam Epitaxy. 1994.
31. Cho, A.Y., GAAS EPITAXY BY A MOLECULAR BEAM METHOD - OBSERVATIONS OF SURFACE STRUCTURE ON (001) FACE. Journal of Applied Physics, 1971. 42(5): p. 2074-&.
32. Plante, M.C. and R.R. LaPierre, Au-assisted growth of GaAs nanowires by gas source molecular beam epitaxy: Tapering, sidewall faceting and crystal structure. Journal of Crystal Growth, 2008. 310(2): p. 356-363.