Amorphous silicon a-Si was made by ion irradiation of crystalline silicon with 1×1015 Xe ions cm–2 at 77 K in the 1–4 MeV energy range. Thermal relaxation of the amorphous network at 500 °C for 1 h leads to an amorphous layer with a refractive index of n = 3.73, significantly higher than that of crystalline silicon (n = 3.45 l at = 1.55 µm). a-Si can thus serve as a waveguide core in Si based optical waveguides. Channel waveguides were made by anisotropic etching of a 1.5 µm silicon-on-insulator structure that was partly amorphized. Transmission measurements of these waveguides as function of the amorphous silicon length show that the a-Si part of the waveguides exhibit a modal propagation loss of 70 cm–1 (0.03 dB µm–1) and a bulk propagation loss of 115 cm–1 (0.05 dB µm–1). Losses due to sidewall roughness are estimated, and are negligible compared to the modal loss.
J. Appl. Phys.
Photonic Materials

de Dood, M., Polman, A., Zijlstra, T., & van der Drift, E. (2002). Amorphous silicon waveguides for microphotonics. J. Appl. Phys., 92, 649–653. doi:10.1063/1.1486055