The mechanisms of absorption in high-gap semiconductors at millimeter and submillimeter wavelengths

A material with very low loss as well as excellent thermal and mechanical properties is required to deliver megawatts of RF power through vacuum windows into the plasma vessel of the ITER fusion reactor. Efforts are being made to acquire the necessary experimental data and extend the available theoretical models to elucidate the predominate mechanisms of absorption for mm and sub-mm electromagnetic waves in high-gap semiconductors, especially CVD diamond and SiC, which are among the most promising low-loss materials commercially available. In order to identify the impurities or defects that give rise to the excess loss, temperature-dependent conductivity and DLTS measurements are being undertaken on SiC. Dielectric loss measurements over a wide range of temperatures are in progress to verify the results obtained from electrical methods and help to determine the primary loss mechanisms for SiC in the millimeter wave length range. Preliminary experimental results will be presented.