本論文主要探討氮化鎵(gallium nitride)奈米線(nanowires)之光電導效率及其物理機制。利用定義歸一化增益，分別探討分子束磊晶與化學汽相沉積氮化鎵奈米線之光電導效率。經由去除實驗參數的貢獻，分子束磊晶成長相較於化學汽相沉積成長之氮化鎵奈米線在光電導效率上約低了100倍，其原因推測是分子束磊晶氮化鎵奈米線有較低的載子濃度以及表面電子捕捉態密度，形成較弱的表面態彎曲效應，使得光電導效率較低。
觀察環境變化暗電導量測探討奈米線之分子效應，發現分子束磊晶成長之氮化鎵奈米線氧氣吸附扮演類施子表面態的角色，與化學汽相沉積成長之氮化鎵奈米線有相同的物理效應。經由次能隙激發源功率相依之光電導量測，在真空環境中表面能帶彎曲增加的現象進一步的被證實，其更加證明分子束磊晶成長之氮化鎵奈米線的光電傳輸特性是由表面能帶彎曲所主導。此外，次能隙激發相對於能隙躍遷，有較低的歸一化增益與量子效率，證明分子束磊晶成長之氮化鎵奈米線有表面態吸收的發生。

In this thesis, we investigated the photoconduction efficiency and physical mechanism of gallium nitride (GaN) nanowires (NWs). The normalized gains, which determine the intrinsic photoconduction efficiencies, were defined and compared for the GaN NWs grown by CVD and MBE. By excluding the contributions of experimental parameters, our results clearly indicated that the magnitude of photoconduction efficiency of MBE-GaN NWs was one hundred times lower than that of CVD-ones. A weaker surface band bending in MBE-GaN NWs due to the lower carrier concentration and lower surface state density in comparison with CVD-NWs is proposed to explain the big difference of the normalized gain.
The molecular effect of GaN NWs was investigated by the environment-dependent dark conductivity measurement. Our results indicate that oxygen molecule plays the role of donor-like surface state in MBE-GaN NWs, which is consistent with previous study for CVD-GaN NWs. By the subbandgap excitation, the model of band bending enhancement in vacuum was further confirmed. The lower normalized gain and quantum efficiency for the subbandgap excitations compared with the band-to-band excitations also indicate the surface state absorption in MBE-GaN NWs.

[1]E. F. Schubert, “Light-emitting diodes”, Cambridge University Press, New York (2006).
[2]H. Amano, N. Sawaki, I. Akasaki, “Metalorganic vapor phase epitaxial growth of a high quality GaN film using an AlN buffer layer”, Appl. Phys. Lett., Vol. 48, pp.353 (1986).
[3]S. Yoshida, S. Misawa, and S. Gonda, “Improvements on the electrical and luminescent properties of reactive molecular beam epitaxially grown GaN films by using AlN-coated sapphire substrates”, Appl. Phys. Lett., Vol. 42, pp.427 (1983).
[4]C. Y. Hwang, “Growth and characterization of gallium nitride on (0001) sapphire by plasma enhanced atomic layer epitaxy and by low pressure metaloganic chemical vapor deposition”, Ph.D. Mechenics and Materials Science, Rutgers University, Piscataway, NJ, (1995).
[5]S. Nakamura, M. Senoh, N. Iwasa, Shin-ichi Nagahama, “High-power InGaN single quantum well structure blue and violet light-emitting diodes”, Appl. Phys. Lett., Vol. 67, pp. 1868 (1995).
[6]S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, Y. Sugimoto, H. Kiyoku, “Room-temperature continuous-wave operation of InGaN multi quantum well structure laser diodes with a long lifetime”, Appl. Phys. Lett , Vol. 70, pp. 868 (1997).
[7]J. W. Orton, C. T. Foxon, “The electron mobility and compensation in n-type GaN”, Semicond. Sci. Technol., Vol. 13, pp. 310 (1998).
[8]史光國, “GaN 藍色發光及雷射二極體之發展現況”, 工業材料, Vol. 126, pp. 154–166 (1997).
[9]Y. Li, J. Xiang, F. Qian, “Dopant-free GaN/AlN/AlGaN radial nanowire heterostructures as high electron mobility transistors”, Nano Lett., Vol. 6, pp.1468–1473 (2006).
[10]S. Nakamura, S. F. Chichibu, “Introduction to nitride semiconductor blue lasers and light emitting diodes”, CRC Press, New York (2000).
[11]賴漢純, “在(111)B GaAs 上成長InGaAs 量子點與量子井結構之螢光光譜分析”, 國立成功大學物理研究所, 碩士論文 (2005).
[12]P. Moriarty, “Nanostructured materials”, Rep. Prog. Phys., Vol. 64, pp. 297–381 (2001).
[13]A. D. Yoffe, “Low-dimensional systems: quantum size effects and electronic properties of semiconductor microcrystallites (zero-dimensional systems) and some quasi-two-dimensional systems”. Adv. Phys., Vol. 42, pp. 173–262 (1993).
[14]X. M. Qian, S. M. Nie, “Single-molecule and single-nanoparticle SERS: from fundamental mechanisms to biomedical applications”, Chem. Soc. Rev., Vol. 37, pp. 912–920 (2008).
[15]S. Nie, S. R. Emory, “Probing single molecules and single nanoparticles by surface-enhanced raman scattering”, Science, Vol. 275, pp. 1102–1106 (1997).
[16]A. A. Bergh, P. J. Dean, “Light-emitting diodes”, Oxford The Clarendon Press, pp. 598 (1976).
[17]M. S. Son, K. H. Yoo, “Ultraviolet photodetector based on single GaN nanorod p-n junctions”, Mater. Sci. Eng.,C, Vol. 26, pp.886–888 (2006).
[18]Matt Law, Lori E. Greene, “Nanowire dye-sensitized solar cells”, Nature Materials, Vol. 4, pp. 455–459 (2005).
[19]M. Asif Khan, A. Bhattarai, J. N. Kuznia, “High electron mobility transistor based on a GaN-AlxGa1-xN heterojunction”, Appl. Phys. Lett., Vol. 63, pp. 1214–1215 (1993).
[20]K. P. Beh, F. K. Yam, C. W. Chin, S. S. Tneh, Z. Hassan, “The growth of III–V nitrides heterostructure on Si substrate by plasma-assisted molecular beam epitaxy”, J. Alloys Compd., Vol. 506, pp. 343–346 (2010).
[21]H. Y. Chen, R. S. Chen, F. C. Chang, L. C. Chen, K. H. Chen, Y. J. Yang, “Size-dependent photoconductivity and dark conductivity of m-axial GaN nanowires with small critical diameter”, Appl. Phys. Lett., Vol. 95, pp. 143123 (2009).
[22]R. S. Chen, C. Y. Lu, K. H. Chen, L. C. Chen,“ Molecule-modulated photoconductivity and gain-amplified selective gas sensing in polar GaN nanowires”, Appl. Phys. Lett., Vol. 95, pp. 233229 (2009).
[23]R. calarco, M. Marso, T. Richter, Ali I. Aykanat, R. Meijers, André v.d. Hart, T. Stoica, H. Lüth, “Size-dependent photoconductivity in MBE-grown GaN-nanowires”, Nano Lett., Vol. 5, pp. 981–984 (2005).
[24]F. Gonzalez-Posada, R. Songmuang, M. Den Hertog, E. Monroy, “Room-temperature photodetection dynamics of single GaN nanowires”, Nano Lett., Vol. 12, pp. 172–176 (2012).
[25]W. P. Halperin, “Quantum size effects in metal particles”, Rev. Mod. Phys., Vol. 58, pp. 533 (1986).
[26]C. Carbonera, F. Luis, “Effect of crystalline disorder on quantum tunneling in the single-molecule magnet Mn12 benzoate”, Phys. Rev. B, Vol. 81, pp. 014427 (2010).
[27]Ball P, Garwin, Laura, “Science at the atomic scale”, Nature, Vol. 355, pp. 761 (1992).
[28]W. P. McCray, “MBE deserves a place in the history books”, Nature Nanotechnology, Vol. 2, pp. 259–261 (2007).
[29]Stephen D. Hersee, “The controlled growth of GaN nanowires”, Nano Lett., Vol. 6, pp.1808–1811 (2006).
[30]P. E. J. Flewitt, R. K. Wild, “Physical methods for materials characterisation”, IOP Publishing, Bristol (1994).
[31]張冠英, “X光能譜分析儀”.
[32]B. D. Cullity, S. R. Stock, “Elements of X-ray diffraction”, Prentice Hall, New Jersey (2001).
[33]H. H. Rose, “Optics of high-performance electron microscopes”, Sci. Technol. Adv. Mater., Vol. 9, pp. 014107 (2008).
[34]K. K. Smith, “Photoluminescence of semiconductor materials”, Thin Solid Films, Vol. 84, pp. 171–182 (1981).
[35]J. P. Wolfe, A. Mysyrowicz, “Excitonic matter”, Scientific American, Vol. 250, pp. 98–107 (1984).
[36]J. I. Pankove, “Optical processes in semiconductors”, Dover Publications, New York (1975).
[37]C. Y. Nam, D. Tham, J. E. Fischer, “Disorder effects in focused-ion-beam-deposited Pt contacts on GaN nanowires”, Nano Lett., Vol. 5, pp. 2029–2033 (2005).
[38]K. P. Beh, F. K. Yam, C. W. Chin, S. S. Tneh, Z. Hassan, “The growth of III–V nitrides heterostructure on Si substrate by plasma-assisted molecular beam epitaxy”, J. Alloys Compd., Vol. 506, pp. 343–346 (2010).
[39]P. Bhattacharya, “Semiconductor optoelectronic devices”, Prentice Hall, New Jersey, Chap. 8, pp. 346–351 (1997).
[40]M. Razeghi, A. Rogalski, “Semiconductor ultraviolet detectors”, J. Appl. Phys., Vol. 79, pp. 7433 (1996).
[41]R. S. Chen, T. H. Yang, H. Y. Chen, L. C. Chen, K. H. Chen, Y. J. Yang, C. H. Su, C. R. Lin, “High-gain photoconductivity in semiconducting InN nanowires”, Appl. Phys. Lett., Vol. 95, pp. 162122 (2009).
[42]H. Y. Chen, R. S. Chen, Nitin K. Rajan, L. C. Chen, K. H. Chen, Y. J. Yang, Mark A. Reed, “Size-dependent persistent photocurrent and surface band bending in m-axial GaN nanowires”, Phys. Rev. B, Vol. 84, pp. 205443 (2011).
[43]C. Fabrega, F. Hernandez-Ramirez, J. D. Prades, R. Jimenez-Diaz, T. Andreu, J. R. Morante, “On the photoconduction properties of low resistivity TiO2 nanotubes”, Nanotechnology, Vol. 21, pp. 445703 (2010).
[44]J. D. Prades, R. Jimenez-Diaz, F. Hernandez-Ramirez, L. Fernandez-Romero, T. Andreu, A. Cirera, A. Romano-Rodriguez, A. Cornet, J. R. Morante, S. Barth, S. Mathur, “Toward a systematic understanding of photodetectors based on individual metal oxide nanowires”, J. Phys. Chem. C, Vol. 112, pp. 14639 (2008).
[45]B. S. Simpkins, M. A. Mastro, C. R. Eddy, Jr., P. E. Pehrsson, “Surface depletion effects in semiconducting nanowires”, J. Appl. Phys., Vol. 103, pp. 104313 (2008).
[46]C. Y. Chang, G. C. Chi, W. M. Wang, L. C. Chen, K. H. Chen, F. Ren, S. J. Pearton, “Electrical transport properties of single GaN and InN nanowires”, J. Electron. Mater., Vol. 35, pp. 738 (2006)
[47]E. Stern, G. Cheng, E. Cimpoiasu, R. Klie, S.Guthrie, J. Klemic, I. Kretzschmar, E. Steinlauf, D. Turner-Evans, E. Broomfield, J . Hyland, R. Koudelka, T. Boone, M. Young, A. Sanders, R. Munden, T. Lee, D. Routenberg, M. A. Reed, “Electrical characterization of single GaN nanowires”, Nanotechnology, Vol. 16, pp. 2941–2953 (2005).
[48]R. S. Chen, S. W. Wang, Z. H. Lan, Jeff T. H. Tsai, C. T. Wu, L. C. Chen, K. H. Chen, Y. S. Huang, C. C. Chen, “On-chip fabrication of well-aligned and contact-barrier-free GaN nanobridge deviceswith ultrahigh photocurrent responsivity”, Small, Vol. 4, pp. 925–929 (2008).
[49]C. Soci, A. Zhang, B. Xiang, S. A. Dayeh, D. P. R. Aplin, J. Park, X. Y. Bao, Y. H. Lo, D. Wang, “ZnO nanowire UV photodetectors with high internal gain”, Nano Lett., Vol. 7, pp. 1003–1009 (2007).
[50]R. S. Chen, C. A. Chen, H. Y. Tsai, W. C. Wang, Y. S. Huang, “Photoconduction properties in single-crystalline titanium dioxide nanorods with ultrahigh normalized gain”, J. Phys. Chem. C, Vol. 116, pp. 4267 (2012).
[51]C. H. Lin, R. S. Chen, T. T. Chen, H. Y. Chen, Y. F. Chen, K. H. Chen, L. C. Chen, “High photocurrent gain in SnO2 nanowires”, Appl. Phys. Lett., Vol. 93, pp. 112115 (2008).
[52]V. Chakrapani, John C. Angus, Alfred B. Anderson, Scott D. Wolter, B. R. Stoner, Gamini U. Sumanasekera, “Charge transfer equilibria between diamond and an aqueous oxygen electrochemical redox couple”, Science, Vol. 318, pp. 1424 (2007).