Influence of sputtering parameters on structural, electrical and thermoelectric properties of Mg-Si coatings

Abstract

Mg-Si thin films (23 ≤ at.% Si ≤ 43) were deposited by co-sputtering of Mg and Si targets in an argon atmosphere. Two groups of samples were prepared with respect to sputtering parameters. The first Group I was synthesized while residual pressure in the reactor was lower than 7 × 10-4 Pa and the second Group II when reactor was pumped down to pressure higher than 7 × 10-4 Pa. The Mg2Si phase appeared for all as-deposited films of Group I around the stoichiometric composition region (29 ≤ at.% Si ≤ 37) and in the Mg-rich region (at.% Si < 29) the Mg2Si and Mg phases coexisted. An amorphous structure was obtained for all as-deposited films of Group II no matter their composition (34 ≤ at.% Si ≤ 38) and the Mg2Si structure was achieved after post annealing under air at temperature ≥140 °C. Thermal stability of Mg2Si thin films was investigated by annealing treatments under air. Superficial Mg2Si structural decomposition began at T > 500 °C and layer morphology and structure damaged while annealing temperature increased up to 700 °C. The films' electrical resistivity, free carrier concentration and mobility as well as Seebeck coefficient were measured and thermoelectric power factors were discussed vs. composition.