Influence Of Heavy Metal Element （Sb,Bi,Sn） Doping On The Thermoelectric Properties Of Cu₂Se Films

Thermoelectric materials are characterized by the direct conversion of heat and electricenergy into each other and have been paid more attentions in the fields of waste heat thermoelectric power generation and electronic refrigeration.Cu₂Se is an ideal thermoelectric material because of its special structure of"electron crystal-phonon glass".The special structure of Cu₂Se material makes it have higher conductivity and lower thermal conductivity.It has a higher thermoelectric figure of merit although its Seebeeck coefficient is slightly lower.By means of element doping,the carrier concentration can be regulated to improve Seebeck coefficient.So the power factor and thermoelectric figure of merit of the material can be further improved.Compared with bulk materials,thin films with approximate low dimensionality can effectively improve the Seebeck coefficient of the material and reduce the thermal conductivity.Thus they show higher thermoelectric properties.In addition,the growth process of thin film is compatible with the production process of semiconductor,so the studies of thin films have higher application value.In this paper,Cu-Se-based alloy targets were prepared by vacuum powder sintering and Cu-Se films doped with Bi,Sb,and Sn elements were deposited on a single-crystal Si substrate containing a silicon oxide insulating layer by magnetron sputtering.The existence state of doping element,microstructure and thermoelectric properties of the deposited films were also studied.The experimental results are as follows:（1）Theβ-Cu₂Se phase films doped with Bi,Sb and Sn were prepared on single-crystal Si substrates containing silicon oxide insulating layers using vacuum-sintered Cu-Se alloy targets.The films doped with Sn and Sb contain onlyβ-Cu₂Se phase and the films doped with 1.07at.%Bi content also contain a small amount ofα-Cu₂Se phase besidesβ-Cu₂Se phase.All deposited films have a highly（111）plane preferred orientation and columnar crystal growth.In the studied doping content range,the doped Bi,Sb,and Sn atoms replace the Cu atoms in theβ-Cu₂Se lattice,formingβ-Cu_2-xM_xSe（M=Bi,Sb,and Sn）solid solution without other secondary phases.The atomic ratio of（Cu+M）/Se in theβ-Cu_2-xM_xSe films are greater than the theoretical value of 2.0,suggesting the deposited films are Cu-rich solid solution films.（2）Allβ-Cu_2-xM_xSe films doped with Bi,Sb,and Sn elements exhibit p-type conductivity characteristics,showing the holes are the majority carriers.For the films doped with Bi and Sn elements,the carrier concentration decreases and the mobility increases with the increase of doping amount.For the Sb-doped films,the carrier concentration tends to frist decrease and then increase,but the mobility tends to increase and then decrease with increasing Sb content.（3）For all depositedβ-Cu_2-xM_xSe films,the conductivity decreases and the Seebeck coefficient increases with increasing measuring temperature.Forβ-Cu_2-xBi_xSe films,the conductivity decreases and Seebeck coefficient increases with increasing Bi content.The deposited films with Bi content of 0.3 at.%have the maximum power factor of 1.34m Wm^-1K^-2at 377℃.Forβ-Cu_2-xSb_xSe films,the Seebeck coefficient decreases and the conductivity shows a trend of frist decreasing and then increasing with increasing Sb content.The films with Sb content of 0.60 at.%have the largest power factor of 0.84 m Wm^-1K^-2at377°C due to the result of competition between the largest Seebeck coefficient and the lowest conductivity.Forβ-Cu_2-xSn_xSe films,the variation of conductivity and Seebeck coefficient with Sn content are the same as those of the films doped with Bi.The film with Sn content of 0.83 at.%has a maximum power factor of 0.93 m Wm^-1K^-2at 400°C.（4）The experiments show that the power factor of the deposited films doped with Bi is the highest,following by the films doped with Sb,and the lowest is the films doped with Sn at the same doping amount.