研究目的
To develop a silicon-compatible fabrication methodology for 3D inverse woodpile photonic crystals with a complete band gap, enabling widespread implementation and applications such as broadband omnidirectional reflectors, waveguides, and optical cavities.
研究成果
A truly silicon-compatible fabrication process for inverse woodpile photonic crystals with a complete band gap has been developed, demonstrated through a broadband omnidirectional reflector. The process yields defect-free, stable crystals using standard equipment, is scalable, and allows for intentional defect introduction for waveguides and cavities, making it suitable for widespread adoption in photonics applications.
研究不足
The process involves a large number of iterative steps (multiple etches, anneals, and epitaxy), which may be time-consuming. Scalability to very small dimensions is limited by the lithography system's critical dimension, though modern tools can achieve features down to tens of nanometers. The proof-of-concept uses relatively large lattice constants (micrometer scale), but the method is adaptable to smaller scales for different wavelength ranges.
1：Experimental Design and Method Selection:
The methodology involves fabricating inverse woodpile photonic crystals using a layer-by-layer process with the empty-space-in-silicon (ESS) technique for the parallel set of cylinders and reactive ion etching (RIE) for the perpendicular set. This includes annealing in a reducing ambient (hydrogen) to form stable air-cylinders through self-limited recrystallization of silicon.
2：Sample Selection and Data Sources:
Silicon wafers are used as the substrate. The design parameters include lattice constants 'a' and 'c', and cylinder radius 'r', with values such as a=
3：5 μm, c=2 μm, r=5 μm in proof-of-concept work. List of Experimental Equipment and Materials:
Equipment includes an Applied Materials reduced-pressure CVD system for annealing and epitaxy, ASML PAS 5500/60 lithography system for trench patterning, and reactive ion etching tools (e.g., Bosch process). Materials include silicon wafers and hydrogen gas for annealing.
4：Experimental Procedures and Operational Workflow:
Steps involve etching trenches using Bosch process, annealing at 1150°C in hydrogen to form air-cylinders, performing silicon homo-epitaxy to add layers, repeating for multiple layers with precise alignment, and finally etching the perpendicular set of cylinders.
5：Data Analysis Methods:
Reflectivity is measured using FTIR spectroscopy, and band structure is computed. FDTD simulations are used for transmission analysis to confirm the complete band gap.
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