Macroporous silicon for spectroscopic CO2 detection

A carbon dioxide sensor based on a photonic crystal of macroporous silicon and measurements of its response are presented in this paper. Photonic crystals have opened new ways for the miniaturization of optical detector devices. In particular, macroporous silicon has proven to be a versatile material for many applications, and more specifically for the creation of photonic crystals in the MIR and NIR spectral regions. In this paper we present the design and fabrication of a MpSi photonic crystal with a photonic stopband in the lambda 4.2 μm region. This bandgap creates a spectral reflection peak centred on one of the main absorption bands for carbon dioxide which can be used to detect the presence of this gas. The device structure is a square lattice of modulated pores with a 700 nm pitch produced by electrochemical etching of silicon. No sensing materials such as polymers are used to perform detection, relying just on the spectral response of as-etched MpSi.