鉍銻碲硒系列拓樸絕緣體長成與物理特性之研究

• Main Authors: 王冠淵, Wang, Kuan Yuan
• Language: 英文
• Published: 國立政治大學
• Subjects: 拓樸絕緣體; Topological Insulator
• Online Access: http://thesis.lib.nccu.edu.tw/cgi-bin/cdrfb3/gsweb.cgi?o=dstdcdr&i=sid=%22G0100755011%22.

三維拓樸絕緣體，其擁有表面可以導電但內部卻屬於絕緣體的特殊性質；近年來成為熱門的研究領域。拓樸保護表面態此種獨特性質使得拓樸絕緣體有潛力成為自旋電子學研究材料。在已發表的文獻中可以得知Bi2Te3系列材料已經被證實為拓樸絕緣體。我們製作了一系列的Bi1.5Sb0.5Te3-ySey材料，希望藉由硒元素的摻雜改變在狄拉克錐體附近的能帶結構以更詳加了解拓樸絕緣體表面性質以及其物理特性。他們的晶格結構為菱形六角面體；當摻雜量y=1.6時，a軸及c軸的晶格常數分別為4.25 Å以及29.80 Å；同時也發現晶格常數隨著硒元素的摻雜量提高而逐漸遞減。為了更進一步了解拓樸絕緣體物理性質，我們做了電阻率、磁阻以及霍爾效應的量測以及分析。電阻率的結果顯示，樣品在高溫時呈現絕緣體的電阻性質，但在低溫時表面態傳導電子開始主導而電阻上升趨勢轉趨於平緩。在霍爾效應中看到低溫至高溫由p-type轉n-type，並且其變化溫度和硒元素摻雜有直接關聯。高溫的n-type載子歸咎於於能隙間的Donor Level受熱後激發電子至傳導帶，最後取代原有的電洞使材料變成n-type。透過阿瑞尼士方程式，可由電阻對溫度曲線計算其活化能，同時可以了解低溫下電阻反曲及載子型態改變之間的關係。我們在磁阻量測中觀察到了弱反局域效應，並且從2 K的數據中顯示此現象和硒元素的摻雜沒有直接關聯性。 === 3D Topological insulator (TI), a type of material that insulates inside bulk and conducts on the surfaces, becomes a popular topic in recent years. The unique topologically protected surface states turn topological insulator to be a potential spintronic material. Bi2Te3 based materials have been studied and identified as topological insulators. In order to study the properties of the surface states, a series of specimens of Bi1.5Sb0.5Te3-ySey (BSTS) with y=1.1, 1.2, 1.4, and 1.6 were fabricated for tuning the band gap around Dirac cone. The lattice structure of Bi1.5Sb0.5Te3-ySey is confirmed to be rhombohedral. For the specimen y=1.4 the lattice constants a ̂ and c ̂are 4.25Å and 29.80Å respectively. The lattice constants decrease with Se substitution increase. To characterize the TI properties, the resistivity, magnetoresistance and Hall effect were studied. Resistivity showed an insulator behavior at high temperatures and surface conduction behavior at low temperatures. The dominate carriers are p-type at low temperatures and become n-type at high temperatures. According to the correlations of resistivity and Hall effect of Bi1.5Sb0.5Te3-ySey, we observed that thermal activation can be tuned by Selenium dopants. The weak anti-localization was also observed in our bulk samples. From the 2 K magnetoresistance, we observed that weak anti-localization was independent on Selenium and Tellurium concentrations in all specimens.