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

Preparation and electrical transport properties of topological insulator(Bi_(1-x)Sb_(x))_(2)Te_(3)thin films

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(Bi_(1-x)Sb_(x))_(2)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(Bi_(1-x)Sb_(x))_(2)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,(Bi_(1-x)Sb_(x))_(2)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,(Bi_(1-x)Sb_(x))_(2)Te_(3)实现了从n型到p型的转化。

In this paper,ultrathin high quality topological insulator(Bi_(1-x)Sb_(x))_(2)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℃and the flow ratio of Bi to Te is 1∶16,high quality(Bi 1-x Sb x)2 Te 3 thin films can be prepared at the Sb temperature of 350,360,370 and 380℃.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(Bi_(1-x)Sb_(x))_(2)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.(Bi_(1-x)Sb_(x))_(2)Te_(3)realizes the transformation from n-type to p-type.