Photonic band engineering in opals by growth of Si/Ge multilayer shells

Engineering the shape of photonic bands is a desirable aim to study anomalous dispersion effects or gap formation. Accurate control of silicon and germanium growth by chemical vapor deposition within thin silica opals is reported here. Alternate layers of the two semiconductors-which can be selectively removed (see Figure)-allows new freedom in the fabrication of photonic crystals (see also cover).