Fabrication of two-dimensional InP photonic band-gap crystals by reactive ion etching with inductively coupled plasma

We fabricated two-dimensional (2D) InP photonic band-gap crystals by reactive ion etching (PIE) with a SiCl4/Ar inductively coupled plasma (ICP) chemistry, and characterized their reflective characteristics in the optical wavelength region by Fourier-transformed infrared reflection absorption spectrometry (FTIR-RAS). The photonic band-gap crystals consisted of a periodic array of parallel air rods of circular cross section whose intersections with a perpendicular plane form a triangular lattice in InP substrates. Prior to the fabrication of the periodic array of air rods, the photonic band structure for electromagnetic waves was calculated theoretically in the sample structure and was predicted to appear in the optical wavelength region. In RIE with the SiCl4/Ar ICP chemistry, we systematically investigated the InP etch rate and the etch selectivity of InP over SiO2 as functions of various etching parameters, to fabricate deep air rods with a vertical profile. The effect of the N2O addition to the SiCl4/Ar ICP chemistry was investigated and it was revealed that the addition of a small amount of N2O results in an improvement in the vertical profile with a slight increase in the InP etch rate. The InP etch rate and the etch selectivity of InP over SiO2 depended strongly on the SiCl4 flow rate. In FTIR-RAS measurements, characteristic features were observed in the optical wavelength region, depending on the diameter of the air rods. Behaviors of the features were discussed in relation to theoretically calculated densities of states.