ABSTRACTCa-Mg-Si films were firstly prepared on (001)Al2O3 substrates by RF-magnetron sputtering method from Mg disc target together with Ca and Si chips. The composition of the deposited films was controlled by adjusting deposition temperature and Ca/Si area ratio of Ca and Si chips on Mg disk target. Ca0.32Mg0.33Si0.35 film deposited at 610 K consisted of a single phase of CaMgSi and this CaMgSi phase was stable after heat treated at 770 K under an atmospheric Ar with 5% -H2. As-deposited film shows the semiconductor behavior and have a power factor of 50 μW/(mK2) at 670 K, while annealed one showed the metallic behavior and its power factor down below 10 μW/(mK2) at 320-770 K. On the other hand, Ca0.27Mg0. 51Si0.2 film deposited at 590 K showed no obvious crystalline phase but became single phase of Ca7Mg7.25Si14 after heat treatment at 770 K under an atmospheric Ar with 5% -H2. As deposited film had a large power factor of 100 μW/(mK2) at 670 K. However, power factor decreased below 1 μW/(mK2) at 320-770K after the heat treatment at 770 K under an atmospheric Ar with 5% -H2.
A RF magnetron sputtering method was used to prepare Mg2Si films at 300-400oC on (001) Al2O3 substrates from a Mg disc target with Si chips. Mg deposition was not detected at 400°C from a pure Mg disc target without Si chips due to the high vapor pressure of Mg. However, the amount of Mg deposition increased with the increase in Si/(Mg+Si) area ratio of the target surface together with the increase of the Si deposition. The obtained films had a stoichiometric composition of Si/(Mg+Si)=0.33 that consisted of the well crystalline Mg2Si single phase regardless of Si/(Mg+Si) area ratio of the target surface. This showed the existence of a “process window” against supply ratio of Si/(Mg+Si) for Mg2Si single phase films with a stoichiometric composition. This is considered to be due to the vaporization of the excess Mg prepared under the Mg excess condition as reported by Mahan et al. for Mg2Si films prepared at 200°C by ultra-high vacuum evaporation.
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