異質介面間會產生許多有趣的物理現象，特別是在一些光電元件或者是光觸媒的應用。因此，了解光照下異質介面間的載子傳輸行為，對於新穎元件無論是在基礎科學亦或是在科技應用面上，是一個重要的研究議題。

本研究論文主要利用超高真空剖面式掃描穿隧顯微鏡，於異質介面處量測異質介面形貌和電子特性。同時，利用雷射照射在異質介面上，量測光激發載子如何在介面處進行傳輸行為，以及在光照下光激發載子如何影響異質介面電子結構。在研究議題上，由於介面處的電子特性與異質結構晶格匹配程度有高度正相關性。因此，在不同的異質介面系統，對於光致載子於異質介面處之傳輸行為進行討論。

第一個研究主題是利用分子磊晶成長氮化鎵在矽(111)基板間的異質介面。在其異質介面處照射光子能量小於氮化鎵能隙的雷射光，量測結果仍可觀察到氮化鎵上面的光致載子的產生，經由理論模擬計算的結果，我們屏除基板上的光激載子，藉由基板和氮化鎵薄膜間的異質介面傳輸到氮化鎵所造成的光致電流之傳輸機制。然而，在氮化鎵薄膜上的高濃度缺陷，提供光激載子的傳輸路徑藉由缺陷能態到氮化鎵薄膜上，形成光電流。同時，利用超高真空剖面式掃描穿隧顯微鏡，我們也呈現實驗結果光致載子傳輸行為如何影響異質介面處電子能帶結構之變化。
第二個研究主題利用凡德瓦爾力吸附在鉑(100)基板上的高介電質單層氧化鈣鈮(Ca2Nb3O10)奈米薄片(nanosheet)以及二氧化矽奈米薄片。二氧化矽從三維限縮到二維奈米呈現隨著缺陷濃度降低的電性差異。在鉑(100)基板上的高介電質單層氧化鈣鈮(Ca2Nb3O10)奈米薄片系統，闡述晶格常數相近異質介面間，因原子堆疊之差異，光致載子傳輸之行為如何改變異質介面上的電子特性。

利用光調制的剖面式穿隧顯微術量測不同異質介面系統，研究成果提供光照下，異質介面電子結構之變化，以及進一步了解光致載子傳輸行為，提供基礎異質介面物理以及元件製程上的重要參考資訊。

The behavior of carrier transport under light illumination at heterointerfaces is an important factor in realizing the basic properties of optoelectronic devices or photocatalytic reaction. In this thesis, light-modulated cross-sectional scanning tunneling microscopy (LM-XSTM) and spectroscopy (XSTS) is utilized to obtain the electronic structures and the change of band alignment at the heterointerface illuminated by a laser. The quality on the growth of heterostructures strongly depends on the lattice mismatch of heterostructures. Therefore, the motivation of my research is to study the behavior of laser-excited carrier at different heterostructures.

My work can separate into two systems of heterostructures: The first system is a heterointerface between GaN films and silicon (111) substrate. The heterointerface consists of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. We probe an obvious increase in the tunneling current during sub-bandgap laser illumination for the GaN layer with high defect density. With the help of a quantitative model to calculate light-excited tunneling, the route for laser-excited carriers generated at silicon across the interface of GaN/Si is excluded. The result of simulation confirms that the laser-excited carriers only generated at the GaN layers are the excitation of free charge carriers at defect states.

The second part is a heterostructure of two-dimensional exfoliated Ca2Nb3O10 (CNO) perovskite nanosheets fabricated on Pt(100) substrate. A Moiré pattern resulting from the interlayer van der Waals interaction is weak to form a lattice-matched coherent heterostructure is observed. Additionally, the band alignments across the heterostructures due to the stacking effect with and without light are illustrated.

The technique of using light-modulated cross-sectional scanning tunneling microscopy is unique to study the behavior of light-excited carriers at heterointerfaces. The fundamental study across the heterointerfaces potentially provides the crucial information for improving the knowledge of fundamental physical properties and the performance of devices at heterostructures.

致謝 ii
中文摘要 iv
Abstract vi
Table of Contents viii
List of Figures Captions xi
Chapter 1 Introduction 1
Chapter 2 Experimental instruments and methods 5
2.1 Principle of Scanning Tunneling Microscopy (STM) 5
2.2 Scanning Tunneling Spectroscopy (STS) 8
2.3 Cross-sectional scanning tunneling microscopy (X-STM) 9
2.4 Light-modulated scanning tunneling microscopy (LM-STM) 10
Chapter 3 Experimental data analysis and the background of theoretical simulation 12
3.1 Theoretical modeling of tunneling current 12
3.1.1 Harrison’s approximation for the calculation of tunneling current 12
3.1.2 Tip-induced band bending (TIBB effect) 15
3.2 Theoretical model for light-excited tunneling 18
3.2.1 Electrostatic potential and carrier distribution 18
3.2.2 Carrier generation and recombination 22
3.2.3 Calculation of the tunneling current 24
Chapter 4 Heterostructures of GaN/Si(111) 26
4.1 Introduction 26
4.2 Sample preparation of GaN on Silicon 28
4.3 Experimental results and discussion 30
4.3.1 Defect characterization using TEM and Cathodoluminescence 30
4.3.2 Cross-sectional STM topography image 34
4.3.3 Photo-excited STS at GAN/Si(111) 37
4.3.4 The mechanism of excited carriers across the interfaces 39
4.3.5 The generation of electron/hole pairs at GaN 45
4.4 Summary 47
Chapter 5 Heterostructures of the Ca2Nb3O10 nanosheet on Pt(100) substrate and two-dimensional atomic nanosheets of titania 49
5.1 Introduction 49
5.2 Sample preparation 51
5.3 Experimental results and discussion 53
5.3.1 STM topography image of the perovskite Ca2Nb3O10 nanosheet 53
5.3.2 Moiré pattern on Ca2Nb3O10 nanosheets 55
5.3.3 Electronic structure of Moiré pattern 58
5.3.4 Photo-excited band alignment on Ca2Nb3O10 61
5.4 Characterization on 2D atomic nanosheets of titania 63
5.5 Summary 66
Chapter 6 Conclusion 67
Reference 68
List of publication 74

[1] A. Ohtomo and H.Y. Hwang, Nature 427, 423 (2004).
[2] J. Chakhalian, J.W. Freeland, G. Srajer, J. Strempfer, G. Khaliullin, J.C. Cezar, T. Charlton, R. Dalgliesh, C. Bernhard, G. Cristiani, H.-U. Habermeier, and B. Keimer, Nat. Phys. 2, 244 (2006).
[3] L. Ivanova, S. Borisova, H. Eisele, M. Dähne, A. Laubsch, and P. Ebert, Appl. Phys. Lett. 93, 192110 (2008).
[4] P. Ebert, S. Landrock, Y. Jiang, K.H. Wu, E.G. Wang, and R.E. Dunin-Borkowski, Nano Lett. 12, 5845 (2012).
[5] Y. Nanishi, Y. Saito, and T. Yamaguchi, Jpn. J. Appl. Phys. 42, 2549 (2003).
[6] O. Jani, I. Ferguson, C. Honsberg, and S. Kurtz, Appl. Phys. Lett. 91, 132117 (2007).
[7] J.W. Ager, L.A. Reichertz, Y. Cui, Y.E. Romanyuk, D. Kreier, S.R. Leone, K.M. Yu, W.J. Schaff, andW. Walukiewicz, Phys. Status Solidi 6, S413 (2009).
[8] E. Trybus, G. Namkoong, W. Henderson, S. Burnham, W.A. Doolittle, M. Cheung, and A. Cartwright, J. Cryst. Growth 288, 218 (2006).
[9] A. Yamamoto, M. Tsujino, M. Ohkubo, and A. Hashimoto, Sol. Energy Mater. Sol. Cells 35, 53 (1994).
[10] X.A. Cao, S.J. Pearton, F. Ren, and J.R. Lothian, Appl. Phys. Lett. 73, 1275 (1998).
[11] T.A. Bull, L.S.C. Pingree, S.A. Jenekhe, D.S. inger, and C.K. Luscombe, ACS Nano 3, 627 (2009).
[12] B.H. Hamadani, S. Jung, P.M. Haney, L.J. Richter, and N.B. Zhitenev, Nano Lett. 10, 1611 (2010).
[13] S. Yoshida, Y. Kanitani, R. Oshima, Y. Okada, O. Takeuchi, and H. Shigekawa, Phys. Rev. Lett. 98, 26802 (2007).
[14] D. Salomon, A. Dussaigne, M. Lafossas, C. Durand, C. Bougerol, P. Ferret, and J. Eymery, Nanoscale Res. Lett. 8, 61 (2013).
[15] T. Chien, J. Liu, J. Chakhalian, N.P. Guisinger, and J.W. Freeland, Phys. Rev. B 82, 41101 (2010).
[16] Y.J. Hwang, C.H. Wu, C. Hahn, H.E. Jeong, and P. Yang, Nano Lett. 12, 1678 (2012).
[17] B.C. Huang, Y.T. Chen, Y.P. Chiu, Y.C. Huang, J.C. Yang, Y.C. Chen, and Y.H. Chu, Appl. Phys. Lett. 100, 122903 (2012).
[18] M. Prietsch, A. Samsavar, and R. Ludeke, Phys. Rev. B. Condens. Matter 43, 11850 (1991).
[19] Y.P. Chiu, B.C. Huang, M.C. Shih, J.Y. Shen, P. Chang, C.S. Chang, M.L. Huang, M.-H. Tsai, M. Hong, and J. Kwo, Appl. Phys. Lett. 99, 212101 (2011).
[20] Y.P. Chiu, Y.T. Chen, B.C. Huang, M.C. Shih, J.C. Yang, Q. He, C.W. Liang, J. Seidel, Y.C. Chen, R. Ramesh, and Y.H. Chu, Adv. Mater. 23, 1530 (2011).
[21] Y.P. hiu, M.C. Shih, B.C. Huang, J.Y. Shen, M.L. Huang, W.C. Lee, P. Chang, T.H. Chiang, M. Hong, and J. Kwo, Microelectron. Eng. 88, 1058 (2011).
[22] F.M. Hsiao, M. Schnedler, V. Portz, Y.C. Huang, B.C. Huang, M.C. Shih, C.W. Chang, L.W. Tu, H. Eisele, R.E. Dunin-Borkowski, P. Ebert, and Y.P. Chiu, J. Appl. Phys. 121, 015701 (2017).
[23] B.C. Huang, Y.P. Chiu, P.C. Huang, W.C. Wang, V.T. Tra, J.C. Yang, Q. He, J.Y. Lin, C.S. Chang, and Y.H. Chu, Phys. Rev. Lett. 109, 1 (2012).
[24] M.C. Shih, B.C. Huang, C.C. Lin, S.S. Li, H.A. Chen, Y.P. Chiu, and C.W. Chen, Nano Lett. 13, 2387 (2013).
[25] L. Dou, A.B. Wong, Y. Yu, M. Lai, N. Kornienko, S.W. Eaton, A. Fu, C.G. Bischak, J. Ma, T. Ding, N.S. Ginsberg, L.-W. Wang, A.P. Alivisatos, and P. Yang, Science 349, 1518 (2015).
[26] Y.-P. Chiu, B.-C. Huang, M.-C. Shih, P.-C. Huang, and C.-W. Chen, J. Phys. Condens. Matter 27, 343001 (2015).
[27] O. Takeuchi, S. Yoshida, and H. Shigekawa, Appl. Phys. Lett. 84, 3645 (2004).
[28] R.J. Hamers and K. Markert, Phys. Rev. Lett. 64, 1051 (1990).
[29] Y. Terada, S. Yoshida, O. Takeuchi, and H. Shigekawa, Nat. Photonics 4, 869 (2010).
[30] A. Okada, K. Kanazawa, K. Hayashi, N. Okawa, T. Kurita, O. Takeuchi, and H. Shigekawa, Appl. Phys. Express 3, 1 (2010).
[31] Y. Terada, S. Yoshida, O. Takeuchi, and H. Shigekawa, J. Phys. Condens. Matter 22, 264008 (2010).
[32] Y. Terada, S. Yoshida, A. Okubo, K. Kanazawa, M. Xu, O. Takeuchi, and H. Shigekawa, Nano Lett. 8, 3577 (2008).
[33] S. Yoshida, J. Kikuchi, Y. Kanitani, O. Takeuchi, H. Oigawa, and H. Shigekawa, E-Journal Surf. Sci. Nanotechnol. 4, 192 (2006).
[34] H. Shigekawa, S. Yoshida, O. Takeuchi, M. Aoyama, Y. Terada, H. Kondo, and H. Oigawa, Thin Solid Films 516, 2348 (2008).
[35] H. Shigekawa (Univ. of Tsukuba), O. Takeuchi, Y. Terada and S.Yoshida, Handb. Nanophysics Princ. Methods, 34-1 (2010).
[36] Y. Terada, S. Yoshida, O. Takeuchi, and H. Shigekawa, Adv. Opt. Technol. 2011, 510186 (2011).
[37] S. Yoshida, Y. Kanitani, R. Oshima, Y. Okada, O. Takeuchi, and H. Shigekawa, Jpn. J. Appl. Phys. 47, 6117 (2008).
[38] S. Yoshida, Y. Kanitani, R. Oshima, Y. Okada, O. Takeuchi, and H. Shigekawa, Phys. Rev. Lett. 98, 26802 (2007).
[39] S. Ohnishi and M. Tsukada, Solid State Commun. 71, 391 (1989).
[40] J. Bono and R.H. Good, Surf. Sci. 175, 415 (1986).
[41] R.M. Feenstra, J. Vac. Sci. Technol. B Microelectron. Nanom. Struct. 5, 923 (1987).
[42] W.A. Harrison, Phys. Rev. 123, 85 (1961).
[43] S.M. Sze and K.K. Ng, Physics of Semiconductor Devices (Wiley-Interscience, 2007).
[44] M. Schnedler, V .Portz, P.H. Weidlich, R.E. Dunin-Borkowski, and P. Ebert, Phys. Rev. B 91, 235305 (2015).
[45] R.M. Feenstra, J. Vac. Sci. Technol. B Microelectron. Nanom. Struct. 21, 2080 (2003).
[46] S. Gaan, G. He, R.M. Feenstra, J. Walker, and E. Twoe, J. Appl. Phys. 108, 114315 (2010).
[47] R.M. Feenstra, Y. Dong, M.P. Semtsiv, and W.T. Masselink, Nanotechnology 18, 044015 (2007).
[48] Y. Dong, R.M. Feenstra, M.P. Semtsiv, and W.T.Masselink, J. Appl. Phys. 103, 073704 (2008).
[49] N. Ishida, K. Sueoka, and R.M. Feenstra, Phys. Rev. B - Condens. Matter Mater. Phys. 80, 1 (2009).
[50] S. Selberherr, Analysis and Simulation of Semiconductor Devices (Springer Vienna, 1984).
[51] J.R. Chelikowsky and M.L. Cohen, Phys. Rev. B 14, 556 (1976).
[52] M. Posternak, H. Krakauer, A.J. Freeman, and D.D. Koelling, Phys. Rev. B 30, 4828 (1984).
[53] H. Morkoç, Nitride Semiconductor Devices : Fundamentals and Applications. (Wiley, 2013).
[54] S. Nakamura, T. Mukai, M. Senoh, and N. Iwasa, Jpn. J. Appl. Phys. 31, L139 (1992).
[55] A. Dadgar, M. Poschenrieder, J. Bläsing, K. Fehse, A. Diez, and A. Krost, Appl. Phys. Lett. 80, 3670 (2002).
[56] M. Himmerlich, A. Eisenhardt, S. Shokhovets, S .Krischok, J. Räthel, E. Speiser, M.D. Neumann, A. Navarro-Quezada, and N. Esser, J. Appl. Phys. 104, 171602 (2014).
[57] B. Zhang and Y. Liu, Chinese Sci. Bull. 59, 1251 (2014).
[58] P.H. Weidlich, M. Schnedler, H. Eisele, R.E. Dunin-Borkowski, and P. Ebert, Appl. Phys. Lett. 103, 062101 (2013).
[59] B. Yang, A. Trampert, O. Brandt, B. Jenichen, and K.H. Ploog, J. Appl. Phys. 83, 3800 (1998).
[60] T.A. Rawdanowicz and J. Narayan, Appl. Phys. Lett. 85, 133 (2004).
[61] G. Radtke, M. Couillard, G.A. Botton, D .Zhu, and C.J. Humphreys, Appl. Phys. Lett. 100, 98 (2012).
[62] D. Zhu, D.J. Wallis, and C.J. Humphreys, Reports Prog. Phys. 76, 106501 (2013).
[63] M. Suzuki, T. Uenoyama, and A. Yanase, Phys. Rev. B 52, 8132 (1995).
[64] F.A. Ponce, D.P. Bour, W. Götz, and P.J. Wright, Appl. Phys. Lett. 68, 57 (1996).
[65] A. Béré, P. Ruterana, G. Nouet, A.T. Blumenau, S. Sanna, T. Frauenheim, J. Chen, and J. Koulidiati, Phys. Rev. B 71, 125211 (2005).
[66] R.M. Feenstra, W.A. Thompson, Phys. Rev. Lett. 56, 608 (1986).
[67] P. Ebert, L. Ivanova, S. Borisova, H. Eisele, A. Laubsch, and M. Dähne, Appl. Phys. Lett 94, 062104 (2009).
[68] D. Krüger, S. Kuhr, T. Schmidt, D. Hommel, and J. Falta, Phys. Status Solidi - Rapid Res. Lett. 3, 91 (2009).
[69] H. isele and P. Ebert, Phys. Status Solidi - Rapid Res. Lett. 6, 359 (2012).
[70] S. Grafström, J. Appl. Phys. 91, 1717 (2002).
[71] L. Lymperakis, P.H. Weidlich, H. Eisele, M. Schnedler, J.-P. Nys, B. Grandidier, D. Stiévenard, R.E. Dunin-Borkowski, J. Neugebauer, P. Ebert, and D. Sti, Appl. Phys. Lett. 103, 152101 (2013).
[72] P. Kloth, K. Kaiser, and M. Wenderoth, Nat. Commun. 7, 10108 (2016).
[73] J.M. Ball and A. Petrozza, Nat. Energy 1, 16149 (2016).
[74] M. Landmann, E. Rauls, W.G. Schmidt, M.D. Neumann, E. Speiser, and N. Esser, Phys. Rev. B 91, 035302 (2015).
[75] D.V. Averin and K.K. Likharev, J. Low Temp. Phys. 62, 345 (1986).
[76] J.A. Stroscio, R.M. Feenstra, and A.P. Fein, Phys. Rev. Lett. 57, 2579 (1986).
[77] K.S. Novoselov, A.K. Geim, S.V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, and A.A. Firsov, Science 306, 666 (2004).
[78] A.K. Geim and K.S. Novoselov, Nat. Mater. 6, 183 (2007).
[79] T. Sasaki, M. Watanabe, H. Hashizume, H. Yamada, and H. Nakazawa, J. Am. Chem. Soc. 118, 8329 (1996).
[80] T. Sasaki and M. Watanabe, J. Am. Chem. Soc. 120, 4682 (1998).
[81] R.E. Schaak and T.E. Mallouk, Chem. Mater. 12, 2513 (2000).
[82] R.E. Schaak and T.E. Mallouk, Chem. Mater. 14, 1455 (2002).
[83] J.Y. Kim, I. Chung, J.H. Choy, and G.S. Park, Chem. Mater. 13, 2759 (2001).
[84] M. Osada, K. Akatsuka, Y. Ebina, H. Funakubo, K. Ono, K. Takada, and T. Sasaki, ACS Nano 4, 5225 (2010).
[85] D. Pacilé, J.C. Meyer, Ç.Ö. Girit, and A. Zettl, Appl. Phys. Lett. 92, 133107 (2008).
[86] M. Osada and T. Sasaki, J. Mater. Chem. 19, 2503 (2009).
[87] Z. Liu, K. Ooi, H. Kanoh, W. Tang, and T. Tomida, Chem. Lett. 29, 390 (2000).
[88] Q. Gao, O. Giraldo, W. Tong, and S.L. Suib, Chem. Mater. 13, 778 (2001).
[89] Y. Omomo, T. Sasaki, L. Wang, and M. Watanabe, J. Am. Chem. Soc. 125, 3568 (2003).
[90] X. Yang, Y. Makita, Z. Liu, K. Sakane, and K. Ooi, Chem. Mater. 16, 5581 (2004).
[91] J.G. Bednorz and K.A. Müller, Zeitschrift Für Phys. B Condens. Matter 64, 189 (1986).
[92] J. Kang, J. Li, S.S. Li, J.B. Xia, and L.W. Wang, Nano Lett. 13, 5485 (2013).
[93] Y.-H. Kim, H.-J. Kim, M. Osada, B.-W. Li, Y. Ebina, and T. Sasaki, ACS Appl. Mater. Interfaces 6, 19510 (2014).
[94] Y. Ebina, K. Akatsuka, K. Fukuda, and T. Sasaki, Chem. Mater. 24, 4201 (2012).
[95] M. Osada and T. Sasaki, Adv. Mater. 24, 210 (2012).
[96] B.-W. Li, M. Osada, Y.-H. Kim, Y. Ebina, K. Akatsuka, and T. Sasaki, J. Am. Chem. Soc. 139, 10868 (2017).
[97] E.D.L. Rienks, N. Nilius, H.P. Rust, and H.J. Freund, Phys. Rev. B - Condens. Matter Mater. Phys. 71, 3 (2005).
[98] S. Marchini, S. Günther, and J. Wintterlin, Phys. Rev. B - Condens. Matter Mater. Phys. 76, 1 (2007).
[99] J. Lu, A.H. C.Neto, and K.P. Loh, Nat. Commun. 3, 823 (2012).
[100] M. Kuwabara, D. R. Clarke, and D. A. Smith, Appl. Phys. Lett. 56, 2396 (1990).
[101] M. Flores, E. Cisternas, J.D. Correa, and P. Vargas, Chem. Phys. 423, 49 (2013).
[102] K.M. Ostyn and C.B. Carter, Surf. Sci. 121, 360 (1982).
[103] R. Bonnet, A. Lherbier, C. Barraud, M.L. DellaRocca, P. Lafarge, and J.C. Charlier, Sci. Rep. 6, 1 (2016).
[104] D. DiFelice, E. Abad, C. González, A. Smogunov, and Y.J. Dappe, J. Phys. D. Appl. Phys. 50, 17 (2017).
[105] K. Kim, A. DaSilva, S. Huang, B. Fallahazad, S. Larentis, T. Taniguchi, K. Watanabe, B.J. LeRoy, A.H. MacDonald, and E. Tutuc, Proc. Natl. Acad. Sci. U. S. A. 114, 3364 (2017).
[106] R. Koitz, A.P. Seitsonen, M .Iannuzzi, and J. Hutter, Nanoscale 5, 5589 (2013).
[107] K. Kobayashi, Phys. Rev. B 53, 11091 (1996).
[108] C. Zhang, C.-P. Chuu, X. Ren, M.-Y. Li, L.-J. Li, C. Jin, M.-Y. Chou, and C.-K. Shih, Sci. Adv. 3, e1601459 (2017).
[109] C.J. Chen, Introduction to scanning tunneling microscopy, Vol. 4. Oxford University Press on Demand. (1993)
[110] L. Lymperakis, P. H. Weidlich, H. Eisele, M. Schnedler, J.-P. Nys, B. Grandidier, D. Stievenard, R. E. Dunin-Borkowski, J. Neugebauer, and Ph. Ebert, Appl. Phys. Lett. 103, 152101 (2013).
[111] X.X. Gao, Q.Q. Ge, D.J. Xue, J. Ding, J. Y. Ma, Y. X. Chen, B. Zhang, Y. Feng, L.J. Wang, and J.S. Hu, Nanoscale, 8, 16881-16885 (2016).