Design, fabrication, and testing of an integrated Si-based light modulator

The implementation of efficient Si optical functions has attracted a considerable interest in the last years since it would allow the use of Si technology for the realisation of integrated optoelectronic (OE) 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 (BMFET) integrated in a silicon rib waveguide realised on epitaxial (epi) 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. Modulation is achieved by moving the plasma inside and outside the optical channel by properly changing the bias of the control electrode. The devices have been fabricated using clean room processes fully compatible with ULSI technology. Electrical characterisation shows a strong channel conductivity modulation. Optical measurements confirm the plasma formation in the channel. The distribution of the plasma under different bias conditions has been directly derived from Emission Microscopy analysis. The devices exhibit modulation depths ranging from 68% up to 83% depending on the bias conditions.