A Si optical phase shifter is essential for high-speed optical interconnect and efficient computing. However, a Si optical phase shifter based on the free-carrier effect is facing the fundamental difficulty to achieve its modulation bandwidth beyond 100 GHz because of the tradeoff relationship between the modulation efficiency and optical loss. The huge power consumption and slow switching speed of a thermo-optic phase shifter are also issues for programmable photonic integrated circuits for computing. To overcome this obstacle, we have investigated the hybrid integration of III-V semiconductors on Si photonics platform. In particular, we have proposed a III-V/Si hybrid metal-oxide-semiconductor (MOS) capacitor for phase modulation, where an n-type III-V membrane is bonded on a p-type Si waveguide with a gate oxide. A III-V/Si hybrid MOS capacitor enables electrons accumulation at the III-V MOS interface, contributing to efficient and low-loss optical phase modulation owing to the superior electron-induced refractive index change in III-V to in Si. We will review the recent progress of III-V/Si hybrid optical phase shifter based on MOS capacitor for optical communication as well as emerging computing applications.
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