The improved thermoelectric properties of Mg2Sn/Mg multilayer films with nano-sized period by layer interface

The Mg2Sn/Mg multilayer films with different nano-sized modulation period were successfully prepared on single crystalline Si substrate with 500 nm thickness SiO2 layer by alternately sputtering using high pure metal Mg target and Mg-Sn alloy target. The chemical composition, surface and cross-sectional morphology, phase composition, carrier transport process and thermoelectric properties of deposited films were deeply investigated. The results show that the deposited films possess obvious layered structure, which is composed of metal Mg layer and antifluorite cubic Mg2Sn layer. The atom ratio [Mg]/[Sn]<2.0 in Mg2Sn layer between metal Mg layers and deposited films are p-typed semiconductor due to the existence of Mg vacancy in Mg2Sn lattice. The carrier concentration, mobility and thermal conductivity at room temperature decrease with reducing the modulation period of the multilayer films due to scattering of layer interface, at which depletion layer and built-in electric field form, impeding motion of the carriers. The electrical conductivity slightly decrease, but the Seebeck coefficient, power factor and figure of merit (ZT) greatly increase with reducing modulation period due to the scattering of the carriers. The ZT value of the film with the smallest modulation period of 171 nm reaches 0.51. The introduction of the layer interface greatly strengthens the carrier scattering process and improves the thermoelectric properties of the deposited films. This work demonstrates that introduction of heterogeneous interfaces composed of the same elements into films can effectively improve its thermoelectric properties.