MICROWAVE PROPAGATION IN SEMICONDUCTOR POWDERS - RAYLEIGH LIMIT

Microwave propagation in semiconductors in powder form is a potentially important technique for the characterization of semiconducting materials. The problem also contains valuable insights into the interaction of electromagnetic waves with inhomogeneous media in general. We have chosen powdered silicon to study the behavior of such an inhomogeneous system because of the wide range of electronic parameters available in this material and the ability to vary the permittivity of the grains by varying the temperature and/or the applied dc magnetic field. A series of samples, with grain size ∼100 μm and a wide range of resistivities, was investigated at temperatures from 77 to 300 °K and magnetic fields from 0 to 20 kG. We show that, for samples with room-temperature resistivities exceeding ∼15 Ω cm, the interaction can be satisfactorily formulated in terms of a theoretical model involving an effective depolarizing factor for the powder medium as a whole. The model becomes less quantitatively reliable for samples with lower resistivity, but still predicts all observed features qualitatively.