Dominant Mode Propagation in Ge and Si with Carrier Density Decaying Exponentially in Time (Correspondence)

Nag and Das have recently made a theoretical study of microwave propagation in a semiconductor-filled rectangular waveguide when the semiconductor has a time dependent carrier density. They have assumed ε and σ to be time dependent in the wave equation for the TE₀₁ mode wave and obtained a solution for the electric field E_x by perturbation techniques for small changes in carrier density. An equivalent propagation constant can be obtained for Germanium and Silicon by solving the wave equation for E_x, assuming no time variations in ε and σ, and then later inserting their dependence. This is an implicit physical assumption in an earlier work of Jacobs, et al.