Design, fabrication, and testing of an integrated Si-based light modulator: experimental evidence of plasma redistribution

The implementation of efficient Si-based optical functions has attracted a considerable interest in the last years since it would allow the use of the Si technology for the realisation of integrated optoelectronic devices. We have fabricated and characterised a novel Si-based light modulator working at the standard communication wavelength of 1.54 mum. It consists of a three terminal Bipolar Mode Field Effect Transistor integrated with a silicon RIB waveguide on epitaxial Si wafers. The optical channel of the modulator is embodied within its vertical electrical channel. Light modulation is obtained through the formation of a plasma of carriers, inside the optical channel, that produces an increase of the absorption coefficient. Fast modulation is achieved by moving the plasma inside and outside the optical channel by properly biasing the control electrode. The devices have been fabricated using clean room processing. Detailed electrical characterisation and device simulation confirm that strong conductivity modulation and plasma formations in the channel are achieved. The plasma distribution in the device under different bias conditions has been directly derived from Emission Microscopy analysis. The expected device performances in terms of modulation depth and speed will be presented and discussed.