Study On The Thermoelectic Properties Of Bi₂T₃ Thin Films Fabriacted By Magnetron Sputter

With the development of modern technology and the increasing of the demand of energy,the research on thermoelectric materials has been given much attention in the last decade.Thermoelectric material can convert heat into electricity directly or vice versa.It has been widely used for thermoelectric generators and thermoelectric coolers.Thermoelectric semiconductor materials have some excellent properties,including the small size,light in weight,long lifetime,easy to control and lack of noise.Bismuth telluride based thermoelectric materials have high thermoelectric efficiency near room temperature,and the figure of merit ZT is close to 1.In recent years,the research of thermoelectric material has gotten new progress by nanotechnology.The carrier concentration and phonon scattering of thermoelectric materials can be increased through reducing dimensions.Then the Seebeck coefficient can be improved and the thermal conductivity decreased.Subsequently,the figure of merit ZT of thermoelectric materials will be improved.The Bi₂Te₃ film belongs to typical two-dimensional structure,and the thermoelectric properties of Bi₂Te₃ can be improved.So it has great value to fabricate Bi₂Te₃ films and research the performance.In this paper,the Bi/Te multilayer thin films with different layers and thickness were designed according to the structure of film.And the Bi/Te multilayer thin films were deposited on glass substrate by magnetron sputtering at room temperature.The annealing process plays an important role for the quality of semiconductor material.The thermoelectric properties of thin film can be improved by the annealing process,which can adjust their surface defects,carrier concentration and grain size.Firstly,the effect of annealing temperature on microstructure and thermoelectric properties of Bi/Te multilayer thin films was studied.The range of annealing temperature was from 0?to250?.The results show that interdiffusion between Bi and Te atoms in adjacent interface is promoted after annealing.The Bi/Te multilayer thin films are transformed into Bi2Te3 films.The grain size increases with the increasing of the annealing temperature.The Seebeck coefficient and power factor increased first and then decreased.The maximum Seebeck coefficient(-98.5?VK^-1)and power factor(14.47?VK^-2cm^-1)can be obtained for the Bi/Te multilayer thin film annealed at 150??Secondly,the effect of annealing time on the microstructure and thermoelectric properties of Bi/Te multilayer thin films was studied.The quantity of interface voids and the surface roughness increase significantly with the increase of annealing time.The thermoelectric properties of thin films can be improved by annealing for a short time.However,the carrier concentration,mobility,conductivity and Seebeck coefficient of Bi/Te multilayer thin films all appear an oscillatory behavior when the annealing time increases,which is attributed to quantum size effects.Meanwhile,the thicker the thickness of the simple deposited layer,the greater the period of oscillatory will be.The effect of outermost element Bi can be eliminated through different layers and thickness.It can be confirm that the Bi/Te multilayer structure will improve thermoelectric properties of thermoelectric materials.Finally,by controlling Bi and Te sputtering time,several samples with different Te atoms percentage contents were obtained.And the effect of percentage contents of the Te atoms on the thermoelectric properties of thin films was discussed.When Te at.%was60.68%,the maximum power factor 22.16?VK^-2cm^-1 can be obtained.The results show that the Bi/Te multilayer thin films deposited by magnetron sputtering can improve thermoelectric properties of materials in the stoichiometric film annealed at 150?and 2⁶h.The thin film is suit for manufacturing thermoelectric devices.