Fabrication of 3D Photonic Band Gap Crystals from Silicon

Three-dimensional (3D) photonic crystals with a complete 3D band gap are studied to control spontaneous emission, cavity QED and localization [1], they also have favorable reflecting properties for solar cells [2]. Yet, the proliferation of 3D photonic crystals is less than their low-dimensional cousins due to perceived fabrication complexity. Therefore, we present our toolbox to fabricate 3D inverse woodpile crystals from silicon with tunable optical properties. First, we precisely fabricate silicon bar substrates by wet etching. A 3D hard etch mask is structured by FIB milling [3]. Using specially tuned deep reactive ion etching, we etch nanopores in two perpendicular directions to obtain 3D inverse woodpile band gap crystals, including cavity superlattices, see Fig. 1. We discuss the metrology of our nanostructures; we acquire 3D stacks of 2D slices through the crystals by FIB-SEM or synchrotron X-ray tomography [5, 6]. Next, we are setting up a numerical toolbox to compute optical properties directly from real structures - as opposed to utopian parametrized models – where we compute unprecedented optical properties.