title: Propagation losses in undoped and n-doped polycrystalline silicon wire waveguides.
abstract: 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 SiO(2) at a maximum temperature of 1000 degrees 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 x 10(18) cm(-3), whereas the 5 x 10(18) 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%H(2) + 90%N(2)) 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.
authors.affiliation: Institute of Microelectronics, A*STAR (Agency for Science, Technology and Research), 11 Science Park Road, Science Park-II, Singapore 117685. zhusy@ime.a-star.edu.sg
authors.forename: Shiyang
authors.initials: S
authors.lastname: Zhu
authors.forename: Q
authors.initials: Q
authors.lastname: Fang
authors.forename: M B
authors.initials: MB
authors.lastname: Yu
authors.forename: G Q
authors.initials: GQ
authors.lastname: Lo
authors.forename: D L
authors.initials: DL
authors.lastname: Kwong
mesh_terms: D003460:Crystallization; D004867:Equipment Design; D053768:Metal Nanoparticles / Q000737:chemistry; D008670:Metals / Q000737:chemistry; D008855:Microscopy, Electron, Scanning / Q000379:methods; D036103:Nanotechnology / Q000379:methods*; D053770:Nanowires / Q000737:chemistry*; D055095:Optics and Photonics; D012825:Silicon / Q000737:chemistry*; D020349:Surface Plasmon Resonance
chemical_list: D008670:Metals; D012825:Silicon