Wide-band modeling of photoinduced carriers at the end of an open-ended microstrip line

This paper presents a wide-band model describing the behavior of an open-ended microstrip line illuminated at its termination. The photoinduced carriers create a plasma at the end of the line, which modifies the complex dielectric constant and, therefore, also the field configuration. The perturbation due to the illumination is modeled by an optically controllable termination load. Its analytical expression is obtained from the integration of the conductivity predicted by the plasma theory. Measurements made on devices fabricated on a silicon substrate validate the model from 0.01 to 20 GHz for an illumination power density of 4 mW/mm² at a wavelength of 685 nm. The validation includes the extraction of the characteristic impedance, which is a complex value because of the low resistivity wafers used (≈250Ω·cm)