Effects Of Indium Doping On Narrow Gap Semiconductor Bismuth Telluride's Bandgap

The narrow gap semiconductor bismuth telluride?Bi₂Te₃?not only has excellent thermoelectric properties at room temperature but also has infrared absorption properties,considered as a promising infrared functional material.Nowadays researchers have already proved that the thermoelectric and infrared properties of Bi₂Te₃ can be affected by impurity doping.And researches on Bi₂Te₃ films become increasingly popular in recent years because of the typical layered structure of Bi₂Te₃.The objectives of this dissertation are to prepare the indium doped Bi₂Te₃ films(In_xBi_2-xTe₃ films)by vacuum vapor deposition technology,and to study the effect of indium doping on the bandgap and carrier transport of In_xBi_2-xTe₃ films by experiments,which is associated with the infrared and thermoelectric properties.The major contents and results in this dissertation are summarized as follows:1.Firstly,In_xBi_2-xTe₃ films are prepared by the vacuum vapor deposition technology and then treated by annealing process to optimize the quality of films.The scanning electron microscope is used to observe In_xBi_2-xTe₃ films'surface topography and to test their chemical composition.According to experimental results,the preparation of In_xBi_2-xTe₃ films can be optimized and then In_xBi_2-xTe₃ films with high quality and exact chemical composition can be obtained.2.The effect of indium doping on the bandgap of In_xBi₂Te₃ films is studied.Using Tauc relation extrapolation method,the bandgaps of In_xBi_2-xTe₃ films are obtained by processing the films'infrared transmission spectra at the selected wavenumber region from 400 to 4000 cm^-1.The experimental results show that with indium doping proportion increasing,which means the value of x increases from 0 to 0.22,the bandgap of In_xBi_2-xTe₃ films decreases from 0.15 to 0.11eV.It is proved that indium doping can narrow the bandgap of Bi₂Te₃.Besides,the mechanism of the bandgap narrowing is analyzed and discussed.3.The effect of indium doping on the carrier transport of In_xBi_2-xTe₃ films is studied.The experimental results show that the carrier concentration,mobility and conductivity of In_xBi_2-xTe₃ films increase with the value of x increasing from 0 to 0.2 at the same temperature.And during the variation of temperature from 140 to 310 K,the carrier concentration and conductivity of In_xBi_2-xTe₃ films keep increasing,but the mobility decreases a little.These results are explained based on the analysis and discussion of variation of defects and carriers in In_xBi_2-xTe₃.