n-p-n Silicon Lateral Phototransistors for Hybrid Integrated Optical Circuits

An etched mesa silicon lateral phototransistor (EMS-LPT) suitable for detecting the light signal from optical channel waveguides has been designed and fabricated. In this paper both n⁺-p-n⁺ uniform base and n⁺-p-p~-n⁺ double-diffused EMS-LPT's are reported. The photoactive region of the EMS-LPT is highly localized and can be easily coupled either via an evanescent field or to a grating coupler on a channel waveguide. Light coupling, gain, speed, and signal-to-noise ratio of the device are thereby greatly improved. The fabrication techniques of the EMS-LPT's are compatible with those of MOSFET's, permitting integration of multiple EMS-LPT's and MOSFET load transistors to form optically addressed inverters on the same silicon chip. By flip-chip bonding LiNb0₃ and silicon substrates and coupling LiNb0₃ channel waveguides to EMS-LPT's via grating couplers, we produce electrooptic switches with optical input and output.