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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 23 — Nov. 9, 2009
  • pp: 20891–20899

Propagation losses in undoped and n-doped polycrystalline silicon wire waveguides

Shiyang Zhu, Q. Fang, M. B. Yu, G. Q. Lo, and D. L. Kwong  »View Author Affiliations

Optics Express, Vol. 17, Issue 23, pp. 20891-20899 (2009)

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Polycrystalline silicon (polySi) wire waveguides with width ranging from 200 to 500 nm are fabricated by solid-phase crystallization (SPC) of deposited amorphous silicon (a-Si) on SiO2 at a maximum temperature of 1000°C. The propagation loss at 1550 nm decreases from 13.0 to 9.8 dB/cm with the waveguide width shrinking from 500 to 300 nm while the 200-nm-wide waveguides exhibit quite large loss (>70 dB/cm) mainly due to the relatively rough sidewall of waveguides induced by the polySi dry etch. By modifying the process sequence, i.e., first patterning the a-Si layer into waveguides by dry etch and then SPC, the sidewall roughness is significantly improved but the polySi crystallinity is degraded, leading to 13.9 dB/cm loss in the 200-nm-wide waveguides while larger losses in the wider waveguides. Phosphorus implantation causes an additional loss in the polySi waveguides. The doping-induced optical loss increases relatively slowly with the phosphorus concentration increasing up to 1 × 1018 cm−3, whereas the 5 × 1018 cm−3 doped waveguides exhibit large loss due to the dominant free carrier absorption. For all undoped polySi waveguides, further 1–2 dB/cm loss reduction is obtained by a standard forming gas (10%H2 + 90%N2) annealing owing to the hydrogen passivation of Si dangling bonds present in polySi waveguides, achieving the lowest loss of 7.9 dB/cm in the 300-nm-wide polySi waveguides. However, for the phosphorus doped polySi waveguides, the propagation loss is slightly increased by the forming gas annealing.

© 2009 OSA

OCIS Codes
(130.3120) Integrated optics : Integrated optics devices
(230.3990) Optical devices : Micro-optical devices
(230.7370) Optical devices : Waveguides

ToC Category:
Integrated Optics

Original Manuscript: July 28, 2009
Revised Manuscript: September 8, 2009
Manuscript Accepted: September 9, 2009
Published: October 30, 2009

Shiyang Zhu, Q. Fang, M. B. Yu, G. Q. Lo, and D. L. Kwong, "Propagation losses in undoped and n-doped polycrystalline silicon wire waveguides," Opt. Express 17, 20891-20899 (2009)

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