在三維拓樸絕緣體硒化鉍(Bi2Se3)系統中，由於硒本身在這材料裡會形成空缺缺陷，造成硒化鉍本質上載子濃度與費米能階偏高而表面態效應被壓抑住。為了研究表面態，我們參雜了鍗(Sb)這個元素進入硒化鉍系統已達到調降載子濃度的效果。我們成功的在藍寶石基板與鈦酸鍶基板上成長了參雜鍗的硒化鉍。在藍寶石基板上我們量測一些基本的電性，鈦酸鍶基板則是利用背閘極調控下研究載子傳輸性質。而在超薄拓樸絕緣體薄膜對閘極電壓的場效下，可以觀察到片電阻有巨大的改變，這改變是來自於表面態在超薄膜的狀況下打開一個表面能隙，而在無閘極電壓時的電阻與最大電阻的差異比例約是14000%。
　　另一方面，我們也研究了量測拓樸絕緣體中自旋訊號的方法，其概念類似於自旋閥元件。在拓樸絕緣體與鐵磁層之間的絕緣層為影響是否能量測到自旋訊號的重要因素。在選用最佳的絕緣層材料與厚度後，我們即可量測到來自表面態類似磁滯曲線的自旋訊號。
　　未來若能夠將此自旋閥元件結合閘極調控與超薄拓樸絕緣體薄膜，在自旋電晶體的應用又更能趨於實踐。

Three-dimensional topological insulator Bi2Se3 has natural Se vacancy and causes high intrinsic n-type carrier concentration. In order to research the surface state, we doped Sb into Bi2Se3 to tune down the carrier concentration. We successfully grew the ultra-thin Sb-doped Bi2Se3 film on sapphire and SrTiO¬3 (STO) substrate, do the basic electrical properties on sapphire and gate-tunable transport properties on STO. An extremely large change of the sheet resistance in ultra-thin film is observed owing to the surface gap opening. The on-off ratio is about 14000%.
On the other hand, we study the spin valve device which can electrical detect the current-induced spin polarization due to spin-momentum locking. The barrier between topological insulator and ferromagnetic layer is the key point to detect the signal. By selecting a great barrier condition, we can observe the hysteresis-like spin signal from surface state.
If we can combine the spin valve device with back gate and ultra-thin topological insulator film, the mechanism of spin-transistor may be realized.

[1] J. E. Moore. The birth of topological insulators. Nature 464, 194 (2010).
[2] X. L. Qi, S. C. Zhang. Topological insulators and superconductors. Rev. Mod. Phys. 83, 1057 (2011).
[3] S. K. Mishra et al. Electronic structure and thermoelectric properties of bismuth telluride and bismuth selenide. Condens. Matter 9, 461 (1997).
[4] T. Thonhauser et al. Thermoelectric properties of Sb2Te3 under pressure and uniaxial stress. Phys. Rev. B 68, 085201 (2003).
[5] G. E. Moore. Cramming more components onto integrated circuits. Electronics 38, 8 (1965).
[6] J. E. Moore. Topological insulator: the next generation. Nat. Phys. 5, 378 (2009).
[7] C. L. Kane et al. Quantum spin hall effect in graphene. Phys. Rev. Lett. 95, 226801 (2005).
[8] K. v. Klitzing et al. New method for high-accuracy determination of the fine-structure constant based on quantized Hall resistance. Phys. Rev. Lett. 45, 494 (1980).
[9] B. A. Bernevig, S. C. Zhang. Quantum spin Hall effect. Phys. Rev. Lett. 96, 106802 (2006).
[10] C. L. Kane and E. J. Mele. Z2 Topological order and the quantum spin Hall effect. Phys. Rev. Lett. 95, 146802 (2005).
[11] J. E. Moore and L. Balents. Topological invariants of time reversal invariant band structures. Phys. Rev. B 75, 121306 (2007).
[12] B. A. Bernevig et al. Quantum spin Hall effect and topological phase transition in HgTe quantum wells. Science 314, 1757 (2006).
[13] M. König et al. Quantum spin Hall insulator state in HgTe quantum wells. Science 318, 766 (2007).
[14] L. Fu et al. Topological insulators in three dimensions. Phys. Rev. Lett. 98, 106803 (2007).
[15] L. Fu et al. Topological insulators with inversion symmetry. Phys. Rev. B 76, 045302 (2007).
[16] D. Hsieh et al. A topological Dirac insulator in a quantum spin Hall. Nature 452, 970 (2008).
[17] H. Zhang et al. Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface. Nat. Phys. 5, 438 (2009).
[18] Y. L. Chen et al. Experimental realization of a three-dimensional topological insulator, Bi2Te3. Science 325, 178 (2009).
[19] D. Hsieh et al. Observation of time-reversal-protected single-Dirac-cone topological-insulator states in Bi2Te3 and Sb2Te3. Phys. Rev. Lett. 103, 146401 (2009).
[20] Y. Xia et al. Observation of a large-gap topological-insulator class with a single Dirac cone on the surface. Nat. Phys. 5, 398 (2009).
[21] M. Z. Hasan, C. L. Kane. Colloquium: Topological insulators. Rev. Mod. Phys. 82, 3045 (2010).
[22] D. Hsieh et al. A tunable topological insulator in the spin helical Dirac transport regime. Nature 460, 1101 (2009).
[23] C. Jozwiak et al. Widespread spin polarization effects in photoemission from topological insulators. Phys. Rev. B 84, 165113 (2011).
[24] J. Chen et al. Gate-voltage control of chemical potential and weak antilocalization in Bi2Se3. Phys. Rev. Lett. 105, 176602 (2010).
[25] J. G. Checkelsky et al. Bulk band gap and surface state conduction observed in voltage-tuned crystals of the topological insulator Bi2Se3. Phys. Rev. Lett. 106, 196801 (2011).
[26] Y. S. Kim et al. Thickness-dependent bulk properties and weak antilocalization effect in topological insulator Bi2Se3. Phys. Rev. B 84, 073109 (2011).
[27] S. Hikami, A. I. Larkin and Y. Nagaoka, Spin-orbit interaction and magnetoresistance in the two dimensional random system. Prog. Theor. Phys. 63, 707 (1980).
[28] J. Tian et al. Quantum and classical magnetoresistance in ambipolar topological insulator transistors with gate tunable bulk and surface Conduction. Sci. Rep. 4, 4859 (2014).
[29] Z. H. Wang et al. Granularity controlled nonsaturating linear magnetoresistance in topological insulator Bi2Te3 films. Nano Lett. 14, 6510 (2014).
[30] Y. S Hor et al. Superconductivity in CuxBi2Se3 and its implications for pairing in the undoped topological insulator. Phys. Rev. Lett. 104, 057001 (2010).
[31] F. Wilczek. Majorana returns. Nat. Phys. 5, 614 (2009).
[32] 詹東霖，國立成功大學碩士論文 (2012).
[33] 沈士育，國立成功大學碩士論文 (2012).
[34] 周昱恆，國立成功大學碩士論文 (2013).
[35] 陳品卉，國立成功大學碩士論文 (2013).
[36] 陳威寧，國立成功大學碩士論文 (2013).
[37] 陳奕帆，國立成功大學碩士論文 (2014).
[38] 王柏雄，國立成功大學碩士論文 (2015).
[39] 林明昱，國立成功大學碩士論文 (2015).
[40] Y. H. Liu, C. W. Chong et al. Gate-tunable coherent transport in Se-capped Bi2Se3 grown on amorphous SiO2/Si. Appl. Phys. Lett. 107, 012106 (2015).
[41] J. Zhang et al. Band structure engineering in (Bi1−xSbx)2Te3 ternary topological insulators. Nat. Comm. 2, 574 (2011).
[42] L. Xue et al. First-principles study of native point defects in Bi2Se3. AIP Adv. 3, 052105 (2013).
[43] S. Cho et al. Antisite defects of Bi2Te3 thin films. Appl. Phys. Lett. 75, 1401 (1999)
[44] D. X. Qu et al. Quantum oscillations and Hall anomaly of surface states in the topological insulator Bi2Te3. Science 329, 821 (2010).
[45] N. J. G. Gouto et al. Transport through Graphene on SrTiO3. Phys. Rev. Lett. 107, 225501 (2011).
[46] A. A. Abrikosov. Quantum linear magnetoresistance. Europhys. Lett. 49, 789 (2000).
[47] C. M. Wang, & X. L. Lei. Linear magnetoresistance on the topological surface. Phys. Rev. B 86, 035442 (2012).
[48] M. M. Parish, P. B. Littlewood, Non-saturating magnetoresistance in heavily disordered semiconductors. Nature 426, 162 (2003).
[49] C. H. Li et al. Electrical detection of charge-current-induced spin polarization due to spin-momentum locking in Bi2Se3. Nat. Nanotechnol. 9, 218 (2014).
[50] M. S. Bahramy et al. Emergent quantum confinement at topological insulator surfaces. Nat. Comm. 3, 1159 (2012).
[51] S. Hong et al. Modeling potentiometric measurements in topological insulators including parallel channels. Phys. Rev. B 86, 085131 (2012).
[52] V. Yazyev et al. Spin polarization and transport of surface states in the topological insulators Bi2Se3 and Bi2Te3 from first principles. Phys. Rev. Lett. 105, 266806 (2010).
[53] L. Liu et al. Spin-polarized tunneling study of spin-momentum locking in topological insulators. Phys. Rev. B 91, 235437 (2015).
[54] J. Tang et al. Electrical detection of spin-polarized surface states conduction in (Bi0.53Sb0.47)2Te3 topological insulator. Nano Lett. 14, 5423 (2014).
[55] J. Tian et al. Electrical injection and detection of spin-polarized currents in topological insulator Bi2Te2Se. Sci. Rep. 5, 14293 (2015).
[56] A. Dankert et al. Room temperature electrical detection of spin polarized currents in topological insulators. Nano Lett. 15, 7976 (2015).
[57] J. S. Lee et al. Mapping the chemical potential dependence of current-induced spin polarization in a topological insulator. Phys. Rev. B 92, 155312 (2015).
[58] Y. Shiomi et al. Spin-electricity conversion induced by spin injection into topological insulators. Phys. Rev. Lett. 113, 196601 (2014).
[59] S. Y. Xu et al. Hedgehog spin texture and Berry’s phase tuning in a magnetic topological insulator. Nat. Phys. 8, 616 (2012).
[60] J. C. A. Huang. Ph. D Thesis, University of Illinois (1992).
[61] E. H. Hall. On a new action of the magnet on electrical current. Amer. J. Math. 2, 287 (1879).
[62] S. M. Sze, K. N. Kwok. Physics of semiconductor devices, 3rd ed. John Wiley & Sons. (2006).
[63] J. Tian et al. Electrical injection and detection of spin-polarized currents in topological insulator Bi2Te2Se. Sci. Rep. 5, 14293 (2015).
[64] A. Y. Cho, J. R. Arthur. Molecular beam epitaxy. Prog. Solid State Chem. 10, 157 (1975).
[65] Oxford Vacuum Science High vacuum science and technology. (http://www.oxford-vacuum.com/)
[66] National Cheng Kung University, Center for micro/nano science and technology. (http://cmnst.ncku.edu.tw/bin/home.php)
[67] X-ray absorption spectroscopy from Wikipedia, the free encyclopedia. (https://en.wikipedia.org/wiki/X-ray_absorption_spectroscopy)