Strain-enabled ultra-broadband Ge-based photonic devices for low-cost integration in PICs

Abstract Photonic-integrated circuits (PICs) have become one of the most promising solutions to the burgeoning global data communication and are being envisioned to have revolutionary impact in many other emerging fields. This outlook requires future PICs to be significantly more broadband and cost-effective. The current germanium (Ge)-based active photonic devices in PICs are thus facing a new bandwidth-cost trade-off. Here, we demonstrate ultra-broadband, high-efficiency Ge photodetectors up to 1,630 nm operation wavelength and Ge0.99Si0.01 electro-absorption (EA) modulator arrays with an operating range of ~100 nm from 1,525 to 1,620 nm, using a CMOS-compatible recess-type silicon nitride (SiNx) stressor. The broadband operation could facilitate a wide (>100 nm) window for low-cost Ge modulator-detector co-integration, requiring only a single step of Ge epitaxy and two different SiNx depositions. The broad modulation and co-integration coverage can be entirely shifted to shorter (~1,300 nm) and longer (>1,700 nm) wavelengths with small amounts of Si or tin (Sn) alloying. This proof-of-concept work provides a pathway for PICs towards future low-cost and high-data-capacity communication networks, immediately accessible by designers through foundries.