Microwave Helicon Interferometry in Semiconductor Plasmas

Abstract

A microwave interferometer bridge technique for the study of helicon wave propagation and related transmission phenomena in semiconductor plasmas is described. The bridge arrangement is in effect a microwave version of the classical Rayleigh refractometer. This approach has several important advantages over the conventionally used Fabry‐Perot dimensional resonance technique, particularly where considerable damping is involved. In addition to high sensitivity, the bridge method allows reliable dispersion measurement even under conditions when less than one helicon period is observed. Furthermore, the interferometer bridge can also be used for quantitative investigation of the helicon damping processes. This latter aspect of the helicon problem, so far relatively unexplored in theory and experiment, is considered in some detail. Helicon experiments, performed on a variety of semiconductors at 35 Gc in the temperature range from 78 to 300°K in magnetic fields up to 100 kG, are used to illustrate the various features of the Rayleigh method. In addition, the influence of leakage, as well as a number of modifications of the bridge approach, are discussed.