Microwave response due to light-induced changes in the complex dielectric constant of semiconductors

Cavity perturbation theory was extended to account for light-induced changes in the complex dielectric constant, as a second perturbation, and the equations were used to interpret the microwave response in the advanced method of transient microwave photoconductivity (AMTMP). The equations obtained earlier from a simpler, first cavity perturbation theory, and those derived for simple geometries are shown to be special cases of this more general theory. For AMTMP, the harmonic-oscillator model can account for the changes in the real and imaginary parts of the dielectric constant made by free and trapped electrons, including plasma effects. The decay of the photoconductivity in semi-insulating (SI) GaAs is dominated by changes in the concentration of electrons, and changes in the mobility can be neglected. The difference between CdSe and SI GaAs in regard to changes in the real part of the dielectric constant is due to the substantially larger mobility in SI GaAs.