Investigation into Microwave Absorption in Semiconductors for Frequency-Multiplication Devices and Radiation-Output Control of Continuous and Pulsed Gyrotrons

The results of experimental investigation into the dielectric losses in GaAs, InP:Fe, and Si semiconductor crystals in the millimeter wavelength range (80-260 GHz) using the original precise method of measuring the reflectance and dielectric-loss tangent tan delta based on open high-quality Fabry-Perot cavities are presented. It is shown that the losses in the frequency range from 100 to 260 GHz in ultrapure semiconductor single-crystal GaAs substrates are mainly determined by lattice absorption, while the main loss mechanism in single-crystal silicon is absorption by free carriers; herewith, tan delta approximate to (1-2) x 10(-4)even for a noticeable, at a level of 10(12)cm(-3), free carrier concentration. In contrast with GaAs and Si, tan delta in compensated InP:Fe crystals is almost independent of frequency in the range from 100 to 260 GHz, which is associated with the material conductivity and optimization of microwave semiconductor devices, in particular, frequency-multiplication devices and devices of the controlled emission output of continuous and pulsed gyrotrons.