A phototransistor is a promising candidate as an optical power monitor in Si photonic circuits since the internal gain of photocurrent enables high sensitivity. However, state-of-the-art waveguide-coupled phototransistors suffer from a responsivity of lower than 103 A/W, which is insufficient for detecting very low power light. Here, we present a waveguide-coupled phototransistor consisting of an InGaAs ultrathin channel on a Si waveguide working as a gate electrode to increase the responsivity. The Si waveguide gate underneath the InGaAs ultrathin channel enables the effective control of transistor current without optical absorption by the gate metal. As a result, our phototransistor achieved the highest responsivity of approximately 106 A/W among the waveguide-coupled phototransistors, allowing us to detect light of 621 fW propagating in the Si waveguide. The high responsivity and the reasonable response time of approximately 100 μs make our phototransistor promising as an effective optical power monitor in Si photonics circuits.
@article{arxiv.2111.01792,
title = {Ultrahigh-sensitivity optical power monitor for Si photonic circuits},
author = {Takaya Ochiai and Kei Sumita and Shuhei Ohno and Stéphane Monfray and Frederic Boeuf and Kasidit Toprasertpong and Shinichi Takagi and Mitsuru Takenaka},
journal= {arXiv preprint arXiv:2111.01792},
year = {2023}
}