Vertical multilayer structures based on porous silicon layers for mid-infrared applications

Abstract

In this work, the fabrication of a porous silicon Bragg reflector and vertical cavity on P+ silicon substrate is investigated for applications in spectroscopic sensing in the mid-infrared (Mid-IR) wavelength range. The complex refractive index of porous silicon layers is measured. Optical vertical devices are then fabricated and characterized by Fourier transform infrared (FTIR) spectrophotometry. This work demonstrates the use of electrochemically prepared Bragg reflectors with reflectance as high as 99% and vertical cavity based on porous silicon layers operating in the mid-IR spectral region (up to 8 µm). Experimental reflectance spectra of the vertical cavity structures are recorded as a function of air exposure duration after thermal annealing under nitrogen flux (N2) and results demonstrate that these structures could be used for spectroscopic sensing applications in the mid-IR (2-8 µm) by grafting specific biomolecules on the porous silicon internal surface.

Theoretical Demonstration of the Interest of Using Porous Germanium to Fabricate Multilayer Vertical Optical Structures for the Detection of SF6 Gas in the Mid-Infrared

“…Thus, p HP is set to 80%, and the Bragg reflector total thickness is smaller for lower p LP , and also for a high porosity contrast Δ p between the two pattern layers. These results also highlight the interest in Ge which, in addition to having a wider transparency, offers much lower layer thicknesses than low refractive indices materials [ 34 ].…”

“…These results show the enormous potential of PGe for the fabrication of optical devices based on multilayer structures. Compared to multilayers based on other materials, the maximum reflectance was achieved for a much lower number of layers [ 34 , 39 , 40 ].…”

“…The absorbance of SF 6 in the Mid-IR wavelength range for different SF 6 concentrations was extracted from the Hitran database [ 33 ]. The mid-IR complex refractive index of Ge, n Ge , was taken from [ 34 , 35 ].…”