Phys. Rev. B 58, issue 7 (1998)
Producing excess carriers by photons causes a change in the complex dielectric constant. Cavity perturbation theory was extended to account for this change as a second perturbation, and the equations were used to interpret the microwave response in the advanced method of transient microwave photoconductivity (AMTMP). Because of the generality of these equations, a suitable choice of constants can be used to reduce them to the simpler forms derived earlier with the first cavity perturbation theory as well as those derived earlier for simple geometries. In the context of our AMTMP results, the harmonic oscillator model provides an adequate description of free and trapped electrons including plasma effects in terms of contributions to the real and the imaginary parts of the dielectric constant. The extension of this model to incorporate other types of bound electrons i.e. electron-hole droplets and excitons is presented also. Using data for SI GaAs, we show that the bulk of the conductivity changes can be interpreted only in terms of changes in the concentration of electrons, and changes in the mobility can be neglected during the decay of the conductivity. The different behavior between CdSe and SI GaAs in regard to changes in the real part of the dielectric constant can be related to the magnitude of the mobility for each material. In both cases free and trapped electrons were present but the contribution by free electrons dominated over trapped electrons in SI GaAs, and the reverse occurred in CdSe, which has a substantially smaller mobility.