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 $\delta$ $\approx$ (1 – 2) $\times$ 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.