在V-VI族化合物中，Bi2Se3、Bi2Te3、Sb2Te3已經被知曉為三維拓樸絕緣體，唯獨Sb2Se3是普通絕緣體，結構為正交晶系(orthorhombic)結構，其能隙(band gap)大約為1.2ev，但Bi2Se3與Sb2Se3的異質結構的理論預測還沒有實驗進行探討，這裡我更進一步的探討這異質結構的特性，它或許可以用於穿隧層和閘極介電層，未來它可以結合TI製作自旋電子元件、場效電晶體及穿隧Junction。
我們利用MBE成功地在藍寶石基板成長了三維拓樸絕緣體(Bi2Se3)與普通絕緣體(Sb2Se3)異質結構。接著進行電性及結構的分析，發現雙層結構中的Sb2Se3與單層Sb2Se3在X-ray繞射(XRD)、原子力顯微鏡(AFM)、反射式高能電子繞射(RHEED)都有明顯的差異，說明Sb2Se3長在藍寶石基板(sapphire)與三維拓樸絕緣體(Bi2Se3)上的磊晶情況是不同的。經過XRD的分析，Sb2Se3結構是正交晶系(orthorhombic)結構，並且傾向在(120)方向上成長。有趣地，在表面的分析上有著巨大的改變，單層Sb2Se3呈現的是不均勻的奈米柱形狀而雙層結構中的Sb2Se3呈現的是較平坦的條狀且有三角形的形狀。
另一方面，我們也從電性上探討雙層結構中的Sb2Se3絕緣性及傳輸性質，透過量測發現其I-V curve呈現非線性，說明Sb2Se3造成蕭特基位障，也間接說明Sb2Se3有絕緣特性，其價帶到費米能階的能差則利用紫外光光電子能譜(UPS)量測得到0.95ev，說明其能隙(Band gap)是蠻大的。在傳輸性質方面，透過載子濃度的變化，說明有電荷轉移的現象，並且會影響傳輸的特性，另外，也透過摻雜及三層結構(Bi2Se3/Sb2Se3 /Bi2Se3)使傳輸性質有所提升及改變。
未來若可利用Sb2Se3結合TI製作成各式自旋電子元件，在自旋電晶體及TI異質結構研究上更能趨於實踐。

關鍵字:拓樸絕緣體、異質結構、自旋

Both Sb2Se3 and Bi2Se3 belong to the family of V(Bi, Sb)-VI(Se, Te) compounds. Among the four binary compounds in this family, three are predicted and confirmed to be three-dimensional topological insulators. The exception for Sb2Se3 to be an ordinary insulator is due to the weaker spin orbit coupling and its orthorhombic crystal structure at ambient pressure. However, the theoretical prediction of Sb2Se3-Bi2Se3 heterostructures systems has not been studied experimentally. In this work, we further explore the characteristics of this heterogeneous structure. Maybe Sb2Se3 can be utilized as a tunnel barrier and gate dielectric, which are essential components of many TI devices.
We have demonstrated a successful MBE growth of Bi2Se3-Sb2Se3 heterostructures on sapphire substrate, the analysis of reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD) and atomic force microscopy (AFM) has a significant difference in Sb2Se3 on Bi2Se3/sapphire and on sapphire.
On the other hand, our devices has nonlinear I-V curve by junction analysis, knowing that Sb2Se3 results in a Schottky-Type transport property. We also indicate that charge transfer results in higher carrier concentration are significant at Sb2Se3-Bi2Se3 systems. In addition, the transport properties can be improved and changed by doping and tri-layer structure.
Key word: topological insulator(TI), heterostructures, spin

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