拓扑绝缘体 $ Bi_{1-x}Sb_{x} $_{2}Te_{3}薄膜制备及其电输运性能研究

文章利用分子束外延(molecular beam epitaxy, MBE)法, 在超高真空的条件下, 于蓝宝石衬底上制备超薄的高质量拓扑绝缘体 $ \left(\mathrm{Bi}_{1-x}\mathrm{Sb}_{x}\right)_{2}\mathrm{Te}_{3} $ 薄膜。利用反射高能电子衍射(reflection high-energy electron diffraction, RHEED)仪、X射线衍射(X-ray diffraction, XRD)仪、显微共焦激光拉曼光谱仪(micro confocal laser Raman spectrometer)和X射线光电子能谱(X-ray photoelectron spectroscopy, XPS)仪对不同Sb掺杂量的样品进行表征, 并获得最佳的制备参数。研究结果表明: 衬底温度为460℃时Bi和Te的流量比为1:16左右; 在Sb温度为350、360、370、380℃时, 可以制得高质量的 $ \left(\mathrm{Bi}_{1-x}\mathrm{Sb}_{x}\right)_{2}\mathrm{Te}_{3} $ 薄膜。利用霍尔效应测量系统测量样品的电阻率、霍尔系数、迁移率和载流子浓度; 测量结果表明, $ \left(\mathrm{Bi}_{1-x}\mathrm{Sb}_{x}\right)_{2}\mathrm{Te}_{3} $ 薄膜的载流子浓度和主要载流子类型随x的变化而发生相应的变化, 并伴随着费米能级位置的调谐, 随着x的增加, 在x=0.53到x=0.68的掺杂过程中, 费米能级从导带下移到带隙, 最终进入价带, 多数载流子类型也从自由电子转变成空穴, $ \left(\mathrm{Bi}_{1-x}\mathrm{Sb}_{x}\right)_{2}\mathrm{Te}_{3} $ 实现了从n型到p型的转化。

In this paper, ultrathin high quality topological insulator $ (\mathrm{Bi}_{1-x}\mathrm{Sb}_{x})_{2}\mathrm{Te}_{3} $ thin films were prepared on sapphire substrates by molecular beam epitaxy (MBE) under ultra-high vacuum. The samples with different Sb contents were characterized by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), micro confocal laser Raman spectrometer and X-ray photoelectron spectroscopy (XPS), and the best preparation parameters were obtained. The results show that when the substrate temperature is 460 °C and the flow ratio of Bi to Te is 1:16, high quality $ (\mathrm{Bi}_{1-x}\mathrm{Sb}_{x})_{2}\mathrm{Te}_{3} $ thin films can be prepared at the Sb temperature of 350, 360, 370 and 380 °C. The resistivity, Hall coefficient, mobility and carrier concentration of the samples were measured by Hall effect measurement system. The measurement results show that the carrier concentration and main carrier types of $ (\mathrm{Bi}_{1-x}\mathrm{Sb}_{x})_{2}\mathrm{Te}_{3} $ thin films change with the content of x, and are accompanied by the tuning of Fermi level position. With the increase of x, in the doping process from x=0.53 to x=0.68, the Fermi level moves down from the conduction band to the band gap, and finally enters the valence band. Most carrier types also change from free electrons to holes. $ (\mathrm{Bi}_{1-x}\mathrm{Sb}_{x})_{2}\mathrm{Te}_{3} $ realizes the transformation from n-type to p-type.