Masashi Komabayashi

Effects of Some Additives on Thermoelectric Properties of FeSi2 Thin Films

Effects of some additives (V, Cr, Mn, Co, Ni, Pd, Pt) on thermoelectric properties of FeSi2 thin films were studied. V, Cr or Mn-doped FeSi2 films were of p-type semiconductor and Co, Ni, Pd and Pt-doped FeSi2 films of n-type semiconductor. It was indicated that V or Cr are more suitable additives in thermoelectric properties of p-type FeSi2 than Mn and that Pt is superior to other additives in thermoelectric properties of n-type FeSi2.

The Composition Dependence of Some Electrical Properties of FeSix Thin Films

The composition dependence of the Seebeck coefficients and the microstructures of FeSix thin films were studied. In the region of x 2.08, the Seebeck coefficient is negative. From the results of the d-spacing measurements, it is inferred that the excess Si in the sample with x>2.08 induces structural defects in the FeSi2, which provides the donor.

Composition Dependence of Some Electrical Properties of Fe1-yMySix (M=Cr, Co) Thin Films

The composition dependence of the Seebeck coefficient, electrical resistivity and activation energy associated with acceptor or donor levels of Fe1-yMySix (M=Cr, Co) thin films obtained by rf sputtering were examined. The activation energy associated with defect levels in undoped films were strongly dependent on the composition (x). For Cr-doped or Co-doped films, the activation energy was smaller than that of a undoped film and insensible to x when the impurity density was sufficiently high. It follows that the variation of the defect levels did not influence the activation energy when the impurity levels were shallower than the defect levels. Accordingly, the Seebeck coefficient and electrical resistivity for Cr-doped and Co-doped films are insensible to the composition (x), although they were influenced by the defect density when the electrical polarity of defects and impurities was different.

Change of Structure and Electrical Properties of FeSi2 Thin Film during Annealing

Changes of structure and electrical properties of FeSi2 thin film by annealing at 380-600°C were studied and the crystallization process of the film was discussed. As a result of annealing, transformation from an amorphous phase to FeSi2 crystal occurred at 380-420°C. FeSi2 crystalline in the film was imperfect and the number of defects decreased with increasing annealing temperature. The electrical resistivity, Seebeck coefficient and activation energy associated with acceptor levels increased with increasing annealing temperature throughout the temperature region. These changes in the electrical properties by annealing were explained by the decrease in the number of defects on annealing. Carrier mobilities in the annealed films at various temperatures were deduced from the results of activation energy measurement.