Thermoelectric transport properties, structure investigations and application of doped /spl beta/-FeSi/sub 2/ thin films

For medium and high temperatures thin films of the silicide compound /spl beta/-FeSi/sub 2/ may be used as thermosensitive material due to its high thermopower and thermal stability. The films under investigation were prepared by magnetron sputtering with the Si/Fe ratio of 2.0 and 2.2 on oxidized Si wafer and aluminum oxide ceramic. The doping elements used with doping level of about 0.2-2.4 at% are Co (n-type) and Cr, Al, Mn (p-type). The polycrystalline semiconducting beta-iron disilicide phase was formed during annealing above 750 K as proved by X-ray and electron diffraction. There are indications of formation of an additional phase in dependence on him composition. In-situ measurements of resistivity /spl rho/ and thermopower S in the temperature range up to 1100 K have been carried out. This data library is discussed in terms of the conduction type, the dopant concentration, the Si/Fe ratio and of the annealing cycles. The energy gap was estimated in the case of dominant intrinsic conductivity (i.e. low doping level) being similar to literature values. The activation energies of dopants could be obtained from films with higher doping levels. Calculations based on simple band model within relaxation time approximation are used for interpretation of experimental data. Carrier mobilities and densities are obtained from Hall measurements below 300 K. The films were tested in thermopile structures.