Abstract
We demonstrate low-loss hydrogenated amorphous silicon (a-Si:H) waveguides by hot-wire chemical vapor deposition (HWCVD). The effect of hydrogenation in a-Si at different deposition temperatures has been investigated and analyzed by Raman spectroscopy. We obtained an optical quality a-Si:H waveguide deposited at 230°C that has a strong Raman peak shift at 480 cm−1, peak width (full width at half-maximum) of 68.9 cm−1, and bond angle deviation of 8.98°. Optical transmission measurement shows a low propagation loss of 0.8 dB/cm at the 1550 nm wavelength, which is the first, to our knowledge, report for a HWCVD a-Si:H waveguide.
Highlights
Silicon photonics devices are fast evolving from discrete optical components to complete circuits that will eventually require low-loss waveguide interconnects and devices for high-density integration
We demonstrate low-loss amorphous silicon (a-Si):H waveguides for the telecoms wavelength band using the Hot-wire chemical vapor deposition (HWCVD) process at temperatures compatible with back end of the line (BEOL)
In the Raman spectrum of the amorphous silicon network, the transverse optical (TO) phonon mode is attributed to the short range order (SRO), while the transverse acoustic (TA), longitudinal acoustic (LA), and longitudinal optical (LO) phonon vibration modes are from the structural distortion in the intermediate range order (IRO) network [34]
Summary
Silicon photonics devices are fast evolving from discrete optical components to complete circuits that will eventually require low-loss waveguide interconnects and devices for high-density integration. The reliance of a silicon-on-insulator (SOI) platform for building up active optical devices limits the fabrication freedom in terms of process temperature for the formation of a multilayer photonics platform. Low temperature deposition of low-loss optical materials is essential for building high-density optical integrated circuits. Low temperature plasma enhanced chemical vapor deposition (PECVD) materials such as silica- and nitride-based waveguides have been demonstrated. These materials can achieve low propagation losses, but their low refractive indices (∼1.5 and ∼2.1 at 1.55 μm, respectively) require mode matching to the silicon devices, adding a layer of complexity to the design and fabrication. The N-H bonds can be annealed out at high temperatures close to 1000°C, such processing renders these materials unsuitable for back end of the line (BEOL) processes [3,4]
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