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

TL;DR

This paper theoretically analyzes how free carriers and interface charges affect the optical and electrical properties of fully-etched silicon waveguides with various dielectric claddings, highlighting their impact on device performance.

Contribution

It introduces a comprehensive model combining measured interface charge effects with semiconductor physics and FDTD simulations to evaluate waveguide behavior.

Findings

Interface charges significantly influence waveguide properties.

Free-carrier effects impact both active and passive silicon photonic devices.

The study provides insights for optimizing waveguide design and material selection.

Abstract

We theoretically characterize the free-carrier plasma dispersion effect in fully-etched silicon waveguides, with various dielectric material claddings, due to fixed and interface charges at the silicon-dielectric interfaces. The values used for these charges are obtained from the measured capacitance-voltage (C-V) 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 (FDTD) 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.