本研究是藉由分子束磊晶系統成長拓樸絕緣體薄膜於藍寶石基板，並分析其材料內部結構特性及磁電傳輸性質。我們嘗試系統化製備鉍、碲、硒合金拓樸絕緣體樣品。三元合金的製備中，各元素之間的比例或佔位是影響本品質的重要關鍵。利用X光繞射分析所得的晶格常數由維加德公式計算，我們底定出當鉍碲硒為2:1.96:1.04時，樣品具有較佳的合金結構品質。透過研究鉍、碲、硒三元合金中硒逐漸取代碲的佔位，對於結構及電性所造成的關聯性。藉由拉曼光譜分析，觀察隨著硒/碲的混和比例逐漸增加，鉍碲硒三元合金結構轉變期間，代表垂直 (A_1g^1、A_1g^2) 及水平 (E_g^2) 三種分量的分子震盪變化及摻雜比例之間的關係。隨著原子摻雜佔位的改變，彼此取代之間的交互作用，導致合金樣品中的震盪峰產生分裂的變化，了解其結構和電性與摻雜比例的相關性。
本論文亦呈現磁性拓樸絕緣體樣品的製備。透過改變鉍化硒的比例及銻的摻雜方式，藉此有效的調控費米能階降至導帶底部表面態附近。而後再經由磁性原子鉻的共摻，成功製備出文獻中未曾報導過的銻及鉻共摻於鉍化硒 (Cr-BSS) 的磁性拓樸絕緣體樣品。在此樣品中，我們測到有別以往文獻主張銻及鉻共摻於鉍化碲 (Cr-BST) 的磁性強弱取決於磁性原子置入多寡的論點。從磁電性觀測到了，當銻摻入磁性鉍化硒 (Cr-BS) 有了顯著的提升。發現樣品的磁性雖然源自於鉻，卻可以透過銻的共摻來間接的調控其磁電性質，並非只是單純取決自鉻的含量。並成功製備出費米能階在室溫情況下存在於表面態區域中，且仍保有拓樸性質的磁性樣品。相信此材料對於未來研究外加偏壓的磁性傳輸元件及應用，可以提供一個作為該相關領域參考使用上的可行性。

In this article, we present a study on the structure and electronic properties of a topological insulator grown on sapphire (0001) substrate by molecular beam epitaxy. We first produce Bi2Te3-xSex alloy films with careful control of the mixing ratio of Bi2Se3 to Bi2Te3 by tuning the Bi:Te:Se flux ratio. According to Vegard’s law, the lattice constant gradually decreases as the Se atomic fraction increases, and we achieved better quality ternary alloys at x = 1.04. Through Raman spectroscopy measurements, the in-plane and out-of-plane phonon peaks were shifted to higher energy by increasing the value of x. In the case of x = 2.03, notable splitting of the two high-frequency modes was observed at intermediate compositions. The worst compounds correspond to the irregular configuration by atomic force microscope. The electronic structures demonstrated that the series of samples were still located inside the bulk conduction band, contrary to the discussion in the literature. The p-type exists in the Bi2Te2Se single crystal owing to the suppression of Se vacancies and Bi/Te antisite defect. Furthermore, the starting Bi2Te2Se1+x, with slightly extra Se content, will result in a mixture of Bi2(Te2-xSex)Se with excess Te, which will drive the materials more metallic. Thus, in order to achieve the true insulating bulk Bi2Te2Se as presented by other bulk single crystal, fine tuning of the Se amount in the vicinity of chemical composition of Bi2Te2Se is a necessary step. However, to clarify this point, further investigation is needed.
Furthermore, we systematically investigated both the magnetism and tuning of a Bi2Se3-based topological insulator. Further, the reduction of EF to conduction band minimum into the surface range in a Cr-Bi2Se3 system has never been reported so far at room temperature. Through the transport measured, we observed that the Sb-doped Cr-Bi2Se3 plays a positive role in enhancing the magnetism in the Cr-Bi2Se3 topological insulator. A large enhanced fabrication method of the magnetism and electrical transport by Sb-doping in a Bi2Se3 system is well suited for the magnetic topological insulator field-effect and spintronic device applications.

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