We show that coherent thermal emission from an amorphous SiO2 thin film can be significantly enhanced by placing it on top of a photonic crystal (PC). To demonstrate this principle, we simulated the reflectance and transmittance of a 1 micron thick layer of SiO2 on a 20 layers PC using the scattering matrix method and finite difference numerical computations. Emissivity, calculated using Kirchhoff’s law, reaches unity at a peak wavelength around 10 microns due to overlapping of the PC’s forbidden band with bulk phonon-polariton modes in SiO2. This region of the electromagnetic spectrum is of particular interest for many technological applications as it corresponds roughly to maximum thermal emission from a blackbody at room temperature. In order to validate these theoretical predictions, a PSi multilayer was fabricated by electrochemical dissolution of p-type Si in HF with current density modulated as a function of time to produce alternating layers of two different porosities with different refractive indices. A 1 micron thick layer of SiO2 was then deposited on top of the resulting PC by plasma enhanced chemical vapor deposition (PECVD). Reflectance of the PC was measured at normal incidence using a Fourier Transform Infrared Spectrometer (FTIR) before and after SiO2 deposition and matches the simulations.

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