Quantum Hall Phase Transition And Optoelectronics In Sn-Bi_1.1Sb_0.9Te₂S Topological Insulator Nanodevices

As a new kind of topological material,topological insulators have drawn wide attention in the field of condensed matter physics because of the topological electronic band structure.Three-dimensional topological insulators have unique electronic band structure:the bulk state has a band gap,similar to a narrow band gap semiconductor;the band structure of the surface state shows gapless linear dispersion relation,similar to graphene.For ideal three-dimensional topological insulators,the electronic transport contribution only comes from topological surface states.Topological electrons have good applied prospects for high speed electionic devices and spin polarized electionic devices because of protection of back scattering and unique spin polarization properties.In addition,due to gapless linear dispersion band structure of the surface states,topological insulators have a natural advantage in application of terahertz excitation and broadband light absorbing.Scholars have carried out extensive research and made rapid progress in Bi based topological insulator family and get high quality material with surface states dominating transport.In this thesis,the author is devoted to study highy quality Sn-Bi_1.1Sb_0.9Te₂S topological insulator nanodevice and trys to reveal its internal electronic interaction mechanism and find the application prospect in optoelectronics field.In the first work,we study quantum Hall phase transition with high quality Sn-Bi_1.1Sb_0.9Te₂S topological insulator.The Hall mobility of prepared nanodevices is as high as more than 10000 cm²/Vs,which indicates a two-dimensional quantum system with high purity surface states transport.We observed the quantum Hall effect with high precision quantum Hall plateau.In the highly quantized localized states,the dominant behavior of transport dissipation translate from thermal activation to varrible range hopping at a critical temperature of 20K.In varrible range hopping regime,we study scaling law of quantum Hall plateau-to-plateau tranisition and give a universal coefficient?0.2.We further get the temperature cosfficient p?1.1 of electronic inelastic scattering with weak anti-localization effect and point out the domination of electron-electron interaction in the topological surface states.In the next work,we observed giant nonvolatile photocurrent responses in the Sn-Bi_1.1Sb_0.9Te₂S topological insulator nanodevices.The photo response sensitivity depends on the position of chemical potential of the surface states,and the memory effect can be erased by control gate voltage and temperature.On the basis of the experimental phenomena,we put forward a remote doping mechanism of topological insulator's selfdoping:light excited carriers jump from bulk defect states to conduction band and eventually release into the surface states,which significantly changes surface states transport.We also find that the doping effect can adjust the quantum Hall effect through broading quantum Hall plateau and changing the position of Dirac point.