Research Of Light Element And Compound Doping Bi₂Se₃ Crystals

New quantum states such as topological insulators?TI?have become a new wave of exploration physics since modern times.Those material is different from conventional metals or insulating materials.The surface state of the material has little effect on other factors such as impurities and can be symmetrically protected by time inversion,a property that allows electrons to be transported without dissipation.Some predictions mention that the combination of such materials and other materials?superconductors or magnetic materials?can obtain singular properties,which has meaning in the fabrication of quantum devices and spintronics.Bi₂Se₃,which is representative of three-dimensional materials,is selected as a target in the topological insulator.Compared with other similar materials,Bi₂Se₃ has a simple structure,which makes the synthesis of the phase easy,has a large energy gap and a Dirac single cone on the surface of the material,the system can introduce ferromagnetism and quantum Hall effect is largely caused.However,the Bi₂Se₃ obtained after the test has a gap with the real TI.Most of the Bi₂Se₃ has a Se-vacancy state,the Fermi level shifts between the band gaps,making it difficult for the surface state of the material to pass through the body state.Since the doping is optimized for the impurity electron doping caused by the defect,the surface state contribution in the system can be improved and the band gap can be opened and can be verified by Li doped Bi₂Se₃.It is reported that since the influence of non-magnetic impurities on TI is relatively small,according to the theory,the light element boron and carbon doping in the non-magnetic elements can compensate for the vacancy of the Se-position,and the topological characteristics can be regulated.So we choose Lithium?boron and carbon are separately doped Bi₂Se₃ for discussion.The preliminary discussion on the doping of carbon-containing compounds and Bi₂Se₃ is briefly carried out:One is a carbon-containing compound anhydrous citric acid?C₆H₈O₇?in the compound,and the other is boron carbide?B₄C?.In addition,since Fe-selenium?FeSe?has a simple structure and no toxic substances,it plays an important role in the development of quantum devices.So doping research between FeSe and Bi₂Se₃ is selected.This thesis has following contents:The Li element doped bismuth selenide.The material structure and its electrical transport properties are discussed.The structure of the sample after doping is basically the same as that of the pure sample.The physical property test shows that the pure sample has no metal insulating transition point but all the doped samples have a metal insulating transition temperature point,that is,the surface state contribution of the sample after doping is improved.Boron element and carbon element are respectively doped bismuth selenide and then discuss the material structure and its transport properties.After doping,the samples belong to a layered structure.Both boron and carbon are mainly substituted for Se in Bi₂Se₃,then a small amount of elements mainly exist in the form of intercalating between atom layers.The metal insulation transition temperature point appears in the electrical transport test after the doping of the two elements with bismuth selenide.The magnetoresistance curve has an inflection point at the metal insulation temperature point,that is,the surface state contribution of the material is improved.The sample doped with B exhibits SdH oscillation near the low temperature of 10K under high magnetic field and exhibits n-type semiconductor behavior.At the same time,the shortage of B-doping for Se-bit vacancy compensation is also explained.The magnetic transport tests after doping of the two elements show a transition from diamagnetic to ferromagnetic and have a clear hysteresis loop.It also indicates that the two elements can induce ferromagnetism with Bi₂Se₃.The compound anhydrous citric acid and boron carbide are doped with cerium selenide,respectively.The characteristics of C₆H₈O₇ after doping are similar to those of C doping,which may be related to carbon powder after C₆H₈O₇ is decomposed by high temperature.However,B₄C could not be doped into Bi₂Se₃.After the test,many hetero phases appeared and the raw materials that were not involved in the reaction were directly observed on the surface of the sample.Iron selenium is doped with strontium selenide.The magnetic transport test of the sample after doping showed that as the doping concentration increased,the diamagnetic resistance of the material increased and then weakened.