Study Of Thermal Transfer And Mechanical Properties In Bismuth Telluride Thin Film Using Molecular Dynamics Simulations

In recent years, overheat has become a more and more important problem since thedensity of integration of semiconductor devices being larger and larger. As the bestthermoelectric material at room temperature, bismuth telluride bears the promise forsemiconductor devices cooling. Nanoscale thermoelectric thin films, thelow-dimensional thermoelectric materials whose fabrication is compatible tosemiconductor manufacturing process, are believed to have higher thermoelectricproperties than traditional materials. The thermal transfer and mechanical properties ofthermoelectric thin films have influence on the thermoelectric properties and relialitiesof the devices. However, because of the poor experimental conditions, it is hard to testperformance of nanoscale materials. Molecular dynamics simulations have become apopular technique to investigate the characteristics of nanoscale materials in atomiclevel.In this work, the thermal transfer properties and mechanical properties innanoscale Bismuth Telluride thin films have been studied. The doping and vacancy,which are common in semiconductor process and semiconductor devices, have alsobeen studied to investigate their influences on thermal transper properties andmechanical properties. The results in this work are believed to be helpful fordevelopment of high-ZT materials.To start with, a potential, which is used for molecular dynamics simulation, isfitted and proved according to the structure and properties of Bismuth Telluride. Theresults show that parameters of the potential reflect the interactions of atoms in BismuthTelluride exactly. The lattice parameters and rdf computed by the potential accord withthe experimental values, which reflect the structure of Bismuth Telluride exactly. Theelastic constants computed by the potential accord with experimental values, which canbe used for simulations of mechanical properties. The phonon dos and phonon spectrumcomputed by the potential accord with experimental values, which can be used forsimulations of thermal transfer properties. The surface effects and rdf in BismuthTelluride thin films are also computed with the fitted potential.Thermal transfer properties of bismuth telluride thin films are then studied with thefitted potential. With appropriate models, the cross-plane and in-plane thermalconductivities and their influence factors are studied. The results are then corrected byquantum corrections. The results show that thermal conductivities are lower than thosein bulk materials. The cross-plane thermal conductivities are lower than in-plane ones.The in-plane values are affected by the size of models. The thermal conductivities increase with the thickness of thin films, and decrease with the increase of workingtemperature. The thermal conductivities also decrease with the increase of dopingconcerntration and the increase of the mass of doped atoms. Finally, the thermalconductivities also decrease with the increase of vacancy concerntration.Mechanical properties of Bismuth Telluride thin films are studied with the fittedpotential. The results show that the mechanical properties of Bismuth Telluride areanisotropic. The mechanical properties in Bismuth Telluride thin films are lower thanthose in bulk materials, and decrease with the increases of working temperature. Theelastic modulus in Bismuth Telluride thin films increase with the increase of thethickness, and approach to bulk values. The mechanical properties change little with theincrease of doping concerntration. The mechanical properties decrease with the increaseof vacancy concerntration. While with the same vacancy concerntration, the vacancyrandom distribution models have lower elastic modulus, higher failure strian and higherultimate stress than uniform models.