Fabrication and characterization of GaP photonic crystals for terahertz wave application

We have fabricated GaP two-dimensional photonic crystals (PCs) for terahertz (THz) wave generation by a reactive ion etching in Ar/Cl ₂ gas chemistries. We performed 75-μm-deep etching of GaP, in which Al ₂O ₃ layer is applied as a hard mask with its selectivity as high as 125. We demonstrated the THz-wave generation from the fabricated GaP slab waveguide with the PC structure as a cladding layer under a collinear phase-matched difference frequency generation. In the frequency dependence of THz output power for the PC slab waveguide is seen at around 1.1 THz. From the in-plane transmission spectrum of THz-wave, we confirmed that the THz output characteristics had relation with the photonic structure for THz wave.