Electrical and optical properties of thin Fe1−xCoxSi2 films

Thin Fe1−xCoxSi2 films were prepared by DC sputtering of Co-doped silicide targets and deposition onto heated quartz substrates. Electrical measurements for the determination of resistivity and Hall coefficient were performed in the temperature range from 300 to 25 K by a van der Pauw method. The Hall mobility at room temperature is below 1 cm2 V−1 s−1, indicating a strong influence of the impurities in the samples on the electrical transport properties. The nonlinear dependence of the Hall resistivity versus the magnetic field at low temperatures is explained by a model assuming magnetic ordering. The sign of the Hall coefficient changes from positive to negative with increasing Co concentration in the films. This could be explained by an increasing of the donor concentration in the samples. The observed change of conduction type from n to p in Co-doped samples shifts to lower temperatures by increasing the silicon content. The optical determined direct gap energy shifts linearly with increasing of the Co concentration to lower energies. This result is explained in terms of a virtual crystal field approximation including compositional disorder.