Optically CW-induced losses in semiconductor coplanar waveguides

The authors present a quasi-static analysis of photoinduced wave attenuation in a continuously illuminated coplanar waveguide transmission line on a semiconductor substrate, using a conformal mapping technique. The relevant effects of charge carrier diffusion and surface recombination on photoconductivity and plasma penetration depth have been incorporated into the theory. This allows a quantitative estimate of optically induced losses as a function of the various light-source and substrate parameters by means of numerically calculated diagrams. In the particular case of small-plasma-depth excitation, an appropriate, analytical expression for the light-controlled attenuation constant is presented. Initial experimental results are in relatively good agreement with the theory