Proposal of a Metal–Oxide–Semiconductor Silicon Optical Modulator Based on Inversion-Carrier Absorption

Abstract

A novel silicon optical modulator, originally based on inversion-carrier absorption, with a metal–oxide–semiconductor capacitor structure has been proposed and successfully developed. In this report, we will describe experimental results for a modulator that is fabricated on a silicon-on-insulator (SOI) substrate. The device consists of a 2- to 5-mm-long and 1.5-µm-thick (110) SOI core and a surrounding clad of 1.0-µm-thick buried oxide underneath and doped polysilicon on top. Infrared light absorption by inversion carriers is not large enough in the 1.55 µm wavelength regime. However, an optical response of 0.24% at a gate voltage of 11.5 V is obtained. Preliminary analysis has been also conducted for the potentiality of the optical modulator based on inversion-carrier absorption. It is predicted that this modulator will be more effective in deeper infrared regions unlike other modulators such as the Mach–Zehnder interferometer.