Microwave helicon resonances in n-InSb spheres

Abstract

Microwave resonances in n-type InSb spheres placed in a magnetic field are studied experimentally and analyzed in light of the recently developed theory of Ford and Werner for the interaction of electromagnetic waves with a gyrotropic sphere. The Ford-Werner theory is a generalization of the Mie theory to the case of gyrotropic media. The present study constitutes an experimental check on the Ford-Werner theory, demonstrating that the theory is capable of fitting microwave resonance spectra remarkably well. Magnetic and electric dimensional resonances and plasma-shifted cyclotron resonance of gyrotropic semiconductor spheres are examined for their usefulness as accurate diagnostic measures of various material parameters, such as carrier concentration, the static dielectric constant, and carrier mobility. Special attention is given to establishing the limits of the accuracy of this method. For example, the static dielectric constant of the InSb lattice is found to be 16.8±0.2 from this set of measurements. Good theoretical fits are obtained for the resonance positions and shapes, but not for all of the resonance amplitudes. The discrepancy is attributed to an insufficiently accurate representation of the carrier system resulting from the use of the Drude free-electron model in the present analysis.