Parametrical study of photonic bandgap structures fabricated using laser-assisted chemical vapor deposition

Laser-assisted chemical vapor deposition (LCVD), in combination with 3-D self-assembly of colloidal silica particles, was used to fabricate 3-D photonic bandgap (PBG) structures. Multilayer of colloidal silica particles was formed on silicon substrates using the isothermal heating evaporation approach. A continuous wave (CW) CO₂ laser (10.6 μm wavelength) was used as the energy source in the LCVD process. A silica-core-silicon-shell PBG structure was obtained. This technique is capable of fabricating structures with various PBGs by obtaining different silicon shell thickness with different LCVD parameters. This enables us to engineer the position and width of PBGs by flexibly controlling the core-shell geometry. Face-centered cubic (FCC) PBG structures were composed by "effective atom" of silica-core-silicon- shell. In this study, a series of PBG structures with designed PBGs were obtained with different experimental conditions. Incidence-angle-resolved spectroscopic ellipsometer was used to identify specific PBGs. The refractive indices of the "effective atom" with different silicon-shell thickness were calculated using Bruggeman composite model. The plain-wave expansion was used to simulate the photonic dispersion diagrams, which agreed with the experimental results.