Ultrafast Carrier And Phonon Dynamics In Topological Insulator Thin Films

In 2009,the V-VI compound Bi₂Te₃ and Bi₂Se₃ were predicted to be a new series of three dimensional topological materials.To put this kind of amazing material into use in the fields like spintronics,opto-electronis and quantum computation,researchers have been doing all kinds of research to have a better understanding of the properties of these materials.However,there are still some properties in the carrier and phonon dynamics remain unknown.This dissertation mainly studied the ultrafast carrier and phonon dynamics in Bi₂Te₃ and Bi₂Se₃ thin films.The main contents are listed here:1?We studied the Raman spectra of Bi₂Te₃ thin films with different thickness,and analyzed the phonon peaks'frequency and broadening.2?We acquired the transient reflection signal of Bi₂Te₃ thin films,divided the signal into 5 parts,and fitted the signal.3?The influence of sample thickness and environment temperature on carrier and phono dynamics were studied.When the sample get thicker,the electron-hole recombination process will dominate the stimulated-carrier relaxing process.While the coherent phonon will become more obvious at lower temperature.4?We verified the existence of second surface state in Bi₂Se₃ thin films through the transient reflection spectrum.And analyzed the influence of second surface state on carrier dynamics.5?Bi₂Se₃ thin films grown on three different substrates were studied.It is proved that the substrate will affect the second rise in the transient reflection signal.