GaAs-based woodpile photonic crystal fabricated by two-directional etching method

A complete photonic band gap inhibits light propagation in all directions regardless of the polarization. This likely provides a means of molding light at the level of physical limits. For example, a complete PBG can be applied to construct nanocavities with ultra-high quality (Q) factor while maintaining a small mode volume, and low-loss waveguide. These are useful for the applications, such as thresholdless lasers, nonlinear optics and 3D optics. Only three-dimensional (3D) photonic crystals can possess a complete band gap. However, the application of 3D photonic crystal is restricted because of the difficulties in precisely fabricating the structures in optical wavelength. Here, we report the fabrication of large-area woodpile photonic crystal in GaAs at 1.55 mu m wavelength by two-directional etching method without wafer bonding technique. A woodpile with 40x55x2.25 unit cells is fabricated in a two-patterning process, in which high-resolution electron beam lithography (EBL) defines 2D patterns, and then chemically assisted ion beam etching (CAIBE) provides high-aspect-ratio, anisotropic and deep GaAs etching at an angle of 45 degree relative to the wafer surface. The two-directional etching is a simple method to fabricate high-precision woodpile photonic crystals. The only alignment required in this process is performed by EBL overlay, which has a resolution of less than 30 nm. With our designs of ultra-high-Q nanocavities by unit cell size modulation, we can construct woodpile nanocavities with active materials, such as epitaxially-grown quantum well (QW) and quantum dot (QD) layers, using the same fabrication method without wafer bonding process.