Numerical Analysis of Carrier-Depletion Strained SiGe Optical Modulators With Vertical p-n Junction

Abstract

The modulation characteristics of carrier-depletion strained SiGe optical modulators with a vertical p-n junction are numerically analyzed by technology computer-aided design simulation and finite-difference optical mode analysis. In addition to the strong optical confinement in the vertical direction for the fundamental transverse electric field mode, the vertical p-n junction effectively depletes the strained SiGe layer in which the plasma dispersion effect is enhanced owing to the mass modulation of holes by strain. We predict that a Si 0.7 Ge 0.3 optical modulator exhibits $V_{\pi }L$ at $1.55~\mu \text{m}$ of as small as 0.31 V-cm at a bias voltage of −2 V, which is $\sim 1.8$ times smaller than that of a Si optical modulator. The product of $V_{\pi }L$ and the phase-shifter loss ( $\alpha V_{\pi }L$ ) is also expected to be as low as 18.3 V-dB at −2 V, enabling optical modulation with a 5-dB extinction ratio in a symmetric Mach–Zehnder modulator.