Fabrication of 2-D Infrared Photonic Crystals in Macroporous Silicon

Abstract

The fabrication of photonic band gap materials at micron and submicron lengthscales still poses some problems. Macroporous silicon is a way to meet the requirements of regularity and high index contrast for a 2-D infrared photonic material. The controlled formation of pores in n-type silicon by light-assisted electrochemical etching in hydrofluoric acid can lead to a regular pattern of uniform holes with minimal changes of the pore diameter both between neighboring pores and with depth. To show the feasibility of the approach, we etched a 340 µm deep 2-D square lattice of circular air rods with a lattice constant of 8 µm in an n-type silicon substrate. This structure possesses individual photonic gaps for both polarizations in the infrared region between 250 and 500 cm^-1 (20 – 40 µm). The transmission spectra between 50 and 650 cm^-1 were in good agreement with the theoretical calculated structure. The pore formation technique should allow the fabrication of photonic lattices with a complete 2-D band gap in the middle and near infrared.