Transmission and Thermal Emission in the NO2 and CO Absorption Lines using Macroporous Silicon Photonic Crystals with 700 Nm Pitch

Abstract

Abstract:Macroporous silicon photonic crystals with a cavity in the middle of their structure have been studied in both, transmission and emission. The initial transmittance of the photonic crystals was increased form 4%-6% up to the value of 25%-30% by performing a rear attach of the samples of approximately 160 µm. The use of wafers with 700 nm of pitch allowed us to fabricate the optical response of the photonic crystals in the ranges of 6.4 µm and 4.6 µm, where different gases have their absorption frequency -such as NO2 or CO. The fabricated samples have been also heated in order to evaluate their viability to be used as selective emitters for gas sensing purposes. Results show a good agreement in the position of the respective peak compared to the transmission spectrum. However, further studies have to be done to place the base of the peak as close as possible to the 0% of emission in order to have a better selective emitter. This work is a starting point for gas detection devices using macroporous technology in the mid-infrared, which includes ammonia, formaldehyde, carbon monoxide or nitrous oxide, among others.

Macroporous Silicon Filters, a Versatile Platform for NDIR Spectroscopic Gas Sensing in the MIR

“…Particularly in the case of CO 2 , the quality factor of the peak was enhanced up to 120. In addition, a bandgap enlargement in respect to previous studies 23 was also reported -see Figure 2c-. This led to a greater separation between the transmitted peak and the edges of the bandgap, thereby clearly discriminating the narrow filter within the forbidden band.…”