Investigation of the microwave magnetoplasma matching effect in indium antimonide

Abstract

Reflection and transmission of microwaves normally incident on a magnetized semiconductor plasma are investigated in the presence of a dielectric quarter-wave layer. Faraday geometry is specifically considered, although conclusions of this work can be generalized to other geometries. Experiments are performed on n-type InSb at 35 GHz between 80 and 300 K. Four characteristic effects caused by the presence of the quarter-wave plate are reported. The first of these, referred to as the ’’magnetoplasma matching effect’’, is the nonresonant minimum of reflectivity observed when the applied dc magnetic field is varied. This effect is shown to be observable over a broad range of values of the effective dielectric constant κeff (including extremely large values, e.g., the helicon wave regime), as long as κeff≳0. Observation of this effect provides a direct measure of κeff, independent of particular microscopic models of this function. The second effect is the enhancement of reflected phase shift. The phase as a function of dc magnetic field is found to have a well-defined minimum between cyclotron resonance and magnetoplasma matching conditions. This effect provides a new tool for investigation of electronic parameters in narrow-gap semiconductors. The enhanced phase change is observed even in the evanescent wave regime (κeff<0) —an especially important feature, since the region of evanescence is notoriously inaccessible to measurements. Third, a great enhancement of the power absorbed by the semiconductor half-space is shown to occur over a broad range of parameters. This is important when κeff is very large, so that half-space absorptivity (without the quarter-wave plate) is too small to be measured accurately. Fourth, extremely large enhancement of transmission through a slab (by several orders of magnitude) is observed over a wide range of dc magnetic fields. Finally, limitations of magnetoplasma matching caused by high-order mode generation are discussed.