Terahertz photonic band gap for the transverse-magnetic modes formed by using a planar waveguide structure with a photonic crystal electrode

摘要

We have investigated the terahertz (THz) emission from a semiconductor superlattice placed in a waveguide structure with a photonic crystal surface electrode of a honeycomb lattice pattern. For uniformly applying bias voltages, we inserted a semitransparent Ti film between the superlattice layer and the photonic crystal electrode. It is found that optimization of the sheet resistivity of the Ti layer is crucial to suppress the coupling between the waveguide mode and the surface leaky mode and obtain a clear photonic band gap. When the Ti layer was 40 nm, a large extinction ratio of ~ 120 in the THz emission intensity was obtained at the midgap frequency around 1.7 THz.