High temperature thermoelectric properties of doped iridium silicide thin films

Iridium silicide thin films were prepared as undoped, Fe-doped and Ni-doped material by means of magnetron sputtering and electron beam evaporation. In the as-deposited state the structure of the films was amorphous. Subsequent annealing of binary and of iron-doped films results in crystallization and phase formation passing a metastable state. By contrast the crystallization process of Ni-containing films was characterized by the formation of residual nickel disilicide (/spl delta/-Ni/sub 2/Si) and nickel trisilicide (/spl beta//sub 1/-Ni/sub 3/Si) The electrical resistivity and the thermopower of the films were measured simultaneously during first annealing process at temperatures from 300 K up to 1200 K showing sensitive dependence on the chemical composition of the films and correlations with the phase formation process. In the final state the iron doped films show rather large thermoelectric power factors with maximum values at temperatures >1200 K as a result of the large gap of Ir/sub 3/Si/sub 5/ (1.56 eV). Estimation of thermoelectric efficiency using thermal conductivity of Ir/sub 3/Si/sub 5/ single crystals results in high values of figure of merit at temperatures >1000 K comparable with the best one observed for /spl beta/-FeSi/sub 2/ and MnSi/sub 1.75/. Ni-doped films with a small concentration of nickel silicides showed n-type conduction.