Microstructure And Thermoelectric Properties Of Mg-Si-Sn Thin Films Deposited By Magnetron Sputtering

Mg-Si-Sn thermoelectric material has many advantages,such as low thermal conductivity,high electrical conductivity,excellent thermoelectric performance,the abundance of constituting elements,and non-toxic character,making it an ideal thermoelectric material at medium temperature?400K-800K?.In this paper,Mg-Si-Sn thin films were prepared by magnetron sputtering with Mg-Si-Sn targets.The thin films were analyzed by X-ray diffractometer system?XRD?,field emission scanning electron microscope?FESEM?and LSR-3?Seebeck coefficient and electric resistance tester?.The influences of deposition temperature,sputtering power,Mg content and Sb doping amount on the crystal structure,surface morphology and thermoelectric properties of thin film materials were investigated.The conclusions are listed below:The crystal structure of Mg-Si-Sn thin films affects thermoelectric properties,and the crystal structure is related to the deposition temperature and power.The films of the deposited Mg₂?Sn,Si?solid solution only contain cubic anti-fluorite crystal structure up to deposition temperature of 300°C.Its maximum power factor reaches 0.96mW·m^-1·K^-2.The film of the deposited Mg₂?Sn,Si?solid solution contains cubic anti-fluorite and the orthorhombic mixed crystal structure as deposition temperature ranges from 300°C to 350°C.Its maximum power factor is about 0.44mW·m^-1·K^-2.When the deposition temperature is above 400°C,The film of Mg₂Sn phase and Mg₂Si phase contains orthorhombic and hexagonal crystal structure.The maximum power factor is only 0.17mW·m^-1·K^-2 The crystal structure is also related to sputtering power.The crystal structure of the thin film possesses hexagonal Mg₂Sn phase and Mg₂Si phase as the sputtering power up to 180W.Its resistivity is lower than other samples and Seebeck coefficient is higher.Thus,its power factor is about 0.8mW·m^-1·K^-2 The crystal structure of the thin film transformed into orthorhombic Mg₂?Si,Sn?solid solution with the sputtering power between 180W to 360W,and the maximum power factor is only 0.33mW·m^-1·K^-2.The main miscrostructure of the thin film is metal Sn when the sputtering power is higher than 360W.The results showed that the thermoelectric performance of the films with Mg₂?Sn,Si?solid solution is better than that of the films with compounds Mg₂Sn or Mg₂Si.The Mg content affects the content of Mg₂?Sn,Si?solid solution in Mg-Si-Sn films.The result shows that the film with high Mg content has high content of cubic antifluorite Mg₂?Si,Sn?solid solution,and the maximum power factor is up to 4.0mW·m^-1·K^-2,which is much higher than other samples.Therefore,it has excellent thermoelectric performance.Three control methods of Mg content are used in research process,including direct sputtering of Mg particles,co-sputtering of Mg target and Mg-Si-Sn target,and sequential deposition of Mg target and Mg-Si-Sn target.Among them,the sequential deposition method is the best.Thermoelectric performance can be enhanced by doping.The film with 8.8at.%Sb doping amount has a more dense surface morphology,higher Seebeck coefficient,lower conductivity,higher power factor,and better thermoelectric performance.