Ultrahigh-speed integrated circuits (ICs) and photodiodes for transceivers and receivers (TRx) are required for future large-capacity optical telecommunications and data-communications systems. Our research group investigates InP-based heterojunction bipolar transistors (HBTs) and avalanche photodiodes (APDs) for future optical network sysytems. Utilizing our long experience in research on optical communications systems, we also focus on InP-based high electron mobility transistors (HEMTs) for applications in the terahertz region as well as on GaN-based materials for high-power applications.
InP- or GaN-based compound semiconductors have higher electron mobility, higher saturation electron velocity, and higher breakdown voltage compared to Si. Owing to these excellent electrical properties, electron devices based on these compound semiconductors can provide higher switching speeds, lower power consumption, and higher power operation.
The full device cycle, including epitaxial growth, device fabrication, and measurement, is performed within our research group’s facilities. Furthermore, in collaboration with other research groups at NTT Laboratories, ICs and comprehensive modules are fabricated based on our devices. For example, we have successfully demonstrated the world’s largest multiplied responsivity bandwidth of 168 GHz·A/W for APDs and ft and fmax over 500 GHz for HBTs with 0.2-µm emitter width.
We are working towards creating innovative device technologies to use the material advantages of compound semiconductors. Our target applications include over-100-Gbit/s large-capacity optical communications systems, ultra-broadband wireless communications systems or imaging sensors that use terahertz frequencies, and ultralow-loss power inverters with GaN-based devices.