Low-loss Ge waveguide at the 2-μm band on an n-type Ge-on-insulator wafer

Integrated mid-infrared (MIR) photonics has been widely investigated for the past decade, where germanium (Ge) is a promising optical material in this regime. In this work, we studied the origin of optical losses in Ge waveguides on a Ge-on-insulator (GeOI) wafer fabricated using Smart-cut. We observed that the high optical loss was mainly due to the holes in Ge films, which were generated by crystal defects formed by hydrogen ion implantation for Smart-cut. Furthermore, we found that the carrier concentration profile after the splitting process in remaining Ge films depends on the hydrogen ion implantation energy and initial background doping concentration of Ge wafers. A higher proton implantation energy can lead to deeper penetration of hydrogen ions into Ge films with less damage remaining near the implantation surface, resulting in the successful fabrication of an n-type GeOI wafer with a low carrier density. As a result, we experimentally demonstrated a low-loss Ge waveguide on an n-type GeOI wafer with a propagation loss as low as 2.3 +/- 0.2 dB/cm. This work suggests an approach to tailor the carrier type in a Ge film formed using Smart-cut for large-scale MIR Ge photonic integrated circuits. (C) 2021 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

This study investigates the optical losses in Ge waveguides on a GeOI wafer fabricated using Smart-cut. The high optical loss is mainly attributed to holes in Ge films caused by crystal defects formed during hydrogen ion implantation. The research demonstrates that the carrier concentration profile in remaining Ge films depends on the hydrogen ion implantation energy and initial background doping concentration of Ge wafers.