Improved transmission and thermal emission in macroporous silicon photonic crystals with 700 nm pitch

In this paper we study the transmittance and the emission response of two different macroporous silicon structures with cavities. The aim is to evaluate the viability of these structures to be employed in a future gas sensor device. The transmittance of the samples has been improved by removing around 150 μm of bulk silicon, rising the initial value of 6 % to 29 %, at 6.5 μm. This improvement in the peak's features should translate in a better sensibility in the future gas sensor. Using samples with 700 nm of pitch allowed us to reduce the vertical periodicity and to translate the peak to 4.6 μm, showing similar behavior in both wavelengths. The emissivity of these samples is also reported in this paper. It shows excellent agreement between the transmitted and emitted peaks in both wavelengths. Further work has to be done in order to reduce the offset in the emission spectrum so the sample can operate as a selective emitter. We suggest the possibility of using this structures for gas sensing purposes in two ways. The first one is using the photonic crystals as a filter of a white emitter. If the peak is correctly placed in the target gas absorption lines, its amplitude is reduced due to the interaction with the gas molecules. The second option is using the photonic crystal with a cavity as a selective emitter. That would simplify the gas sensor: the emitter will propagate light in the resonant wavelengths of the studied gas, allowing a future creation of more compact gas sensors.