Electrical Pulse-tuned Thermoelectric Parameters Of Germanium Telluride Nanowires

Introducing nanostructure into materials will have a strong influence on thermal transport and thermoelectric.Due to the Debye model on thermal transport,the thermal transport of semiconductor and insulator is determined by thermal capacity and defects,boundary or Umklapp effect.On the other hand,these effects will also have strong influence on thermoelectric parameters,which will have strong influence on the figure of merit on thermoelectric performance.In addition,we introduce a thermal-bridge method that can measure the thermal and electrical transport parameters,respectively.However,the procedure to introduce nanostructure is usually very complex and it has been proved to be very hard to manipulate and optimize each thermoelectric factors,respectively.Meanwhile,phase change materials,which have been intensively studied and can modify their local structures by laser or electrical pulse,have not been theoretically investigated the relationship between phase change properties and thermal transport and thermoelectric parameters.In this dissertation,we synthesized two different kinds of phase change materials nanowires through chemical vapor deposition method,and characterized them by transmission electron microscope,scan electron microscope,XRD,respectively.We operate the electrical-pulse test on silicon-oxide substrate and suspended bridge,and for the first time we change the Germanium Telluride phase by electrical pulse on the suspended substrate.By investigating the electrical conductivity change versus temperature,we get to know the existence of different phases of Germanium Telluride nanowire and their transport mechanism.Furthermore,we test the Seebeck coefficient of amorphous and crystalline phase Germanium Telluride nanowires,which shows similar amplitude and trend versus temperature,which indicate that the amorphous region is just locally confined in the nanostructure.In addition,the measurement of thermal conductivity of amorphous-phase Germanium Telluride nanowire before and after pulse has been applied,which shows similar numerical value with bulk materials thermal conductivity,as predicted by mean free path.The trend of thermal conductivity and electrical conductivity is different,indicating the optimizations of thermal and electrical transport,respectively.Then,we for the first time determine the thermoelectric figure of merit of amorphous Germanium Telluride nanowire.We can further determine the thermoelectric figure of merit of other phases by applying electrically pulse and make a systematic study.Meanwhile,further determinations of transmission electron microscope and EELS is needed.We also need to simulate the transport phenomenon in order to get a deeper understanding of the pulse-tuned thermoelectric properties.