Si nanowire phototransistors at telecommunication wavelengths by plasmon-enhanced two-photon absorption

The on-chip integration of optical waveguides with complementary metal-oxide-semiconductor (CMOS) transistors is the next generation technology for high-speed communications. The advance of such a technology requires a high-performance photodetector operating at communication wavelengths. However, silicon does not absorb photons at communication wavelengths because of its relatively large bandgap. Growing high quality small bandgap semiconductors on top of silicon is challenging due to lattice mismatch. An all silicon photonic CMOS technology is an attractive option. Here, we demonstrate a high-performance silicon phototransistor that operates at the communication wavelengths by two-photon absorption effect. To turn silicon into a light absorptive material at communication wavelengths, we have designed a sophisticated plasmonic antenna structure to increases the intensity of light in the silicon nanowire by 5 orders of magnitude. At the high light intensity, the light absorption in silicon is dominated by the two-photon absorption effect. The generated photocurrent is further amplified by the Si nanowire phototransistor, a section of which is doped to be a core-shell pn junction. Simulation results indicate that the device can achieve a responsivity of 2.4×10⁴ A/W and a 3-dB bandwidth over 300 GHz. Successful development of such a device is important for the next generation high-speed communication technology.