本實驗以MBE系統在sapphire (0001)基板成長三維拓樸絕緣體Sb2Te3與Bi2Te3，並進一步將其成長為Sb2Te3/Bi2Te3雙層異質結構，拓樸具有絕緣的體能態與導電的表面態，為了更深入研究表面態的傳輸行為與元件的潛力，需要將fermi level 由價帶調控至dirac point附近，此時表面態(surface state)將取代體態(bulk state)成為傳輸主導。要達成這個目的Sb2Te3/Bi2Te3雙層異質結構是個好方法，兩者結構、晶格常數接近，成長上較容易，所以首先我們進行樣品成長的研究，並以多種儀器檢驗成長品質。
接著要驗證fermi level與surface state關係需藉由ARPES進行分析，分析過程中的確fermi level達到dirac point，但因為ARPES只能分析表面無法分析樣品整體，所以需做hall bar元件並以霍爾量測檢測其電性，因Sb2Te3/Bi2Te3兩者分別為n/p-type，隨厚度的調控可使兩者相互擴散在介面處形成三元合金，並調控fermi level位置，在整體carrier type轉變的時候，即為fermi level最接近dirac point的厚度。
另一方面，在光偵測器元件的量測上，原本拓樸絕緣體因為能隙極小，缺乏阻止載體快速復合的障礙，所以難以量測其光學性質，不過Sb2Te3/Bi2Te3異質結構會在介面處形成p-n junction，可有效抑制照光時產生的電子電洞對複合，而在調控厚度進行電性量測實驗中，carrier type轉變的同時，此厚度應會有最大的空乏區產生，而其產生的內建電場將有效使光電流提升，可有效提升拓樸絕緣體在光學上的應用價值，而本實驗也成功證實在電性量測上的carrier type轉變位置，即為光學量測上光響應最大值的所在。

In this research. We grow Sb2Te3/Bi2Te3 heterostructure on sapphire (0001) substrate by the MBE system. At the interface, diffusion of Sb and Bi causes the ternary compounds and tuning fermi level. By adjusting the thickness ,we can tuning Fermi level to the dirac point and form an ideal topological insulator. We confirmed this result through ARPES and hall measurements.
In Hall measurement, carrier type transition occurs between 7/10nm and 8/10nm. The change of carrier type also appeared in ARPES measurement. At this time, Surface state replaces bulk state as the main contributor to carrier transport.
On the other hand, Sb2Te3/Bi2Te3 heterostructure has a p-n junction at the interface. The built-in potential at the interface can effectively separate the electron-hole pairs in TI and suppress the rapid recombination of carriers, leading to an outstanding photo responsivity.
At the same time as the carrier type changes, the largest depletion region will occur at the interface. This can effectively separate the electron-hole pairs , and lead to the maximum photo responsivity.
Finally, we obtain maximum responsivity of the photodetector measured under 632.8 nm light illumination at 7/10 nm Sb2Te3/Bi2Te3. The photodetector possessed a large light responsivity of 167 A/W. The result of photodetector measurement correlates with the conclusion of Hall measurement.

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