Characterizing the effects of free carriers in fully etched, dielectric-clad silicon waveguides

Abstract

We theoretically characterize the free-carrier plasma dispersion effect in fully etched silicon waveguides, with various dielectric material claddings, due to fixed interface charges and trap states at the silicon-dielectric interfaces. The values used for these charges are obtained from the measured capacitance-voltage characteristics of SiO2, SiNx, and Al2O3 thin films deposited on silicon substrates. The effect of the charges on the properties of silicon waveguides is then calculated using the semiconductor physics tool Silvaco in combination with the finite-difference time-domain method solver Lumerical. Our results show that, in addition to being a critical factor in the analysis of such active devices as capacitively driven silicon modulators, this effect should also be taken into account when considering the propagation losses of passive silicon waveguides.