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Experimental evidence of the photonic bandgap and defect effect in Si‐SiO2 multilayer structures

We have elaborated a one dimensional photonic crystal (Si/SiO2) by depositing alternative silicon and silica layers by radiofrequency magnetron sputtering technique with cold plasma. After optimising the layer thickness to get good transmission, we studied the effect of the crystal layers number on the transmission and reflection spectra. We have shown that the photonic bandgap appears after five alternating Si and SiO2 layers and is well structured after nine alternating layers with a pseudo‐band gap of 1.75 eV. We have also introduced a defect in the structure by changing the thickness of one Si layer, than of one SiO2 layer, in the middle of the structure and observed a corresponding defect mode frequency. Using a theoretical model based on the Plane Wave Expansion method and an appropriate code calculation, we have shown that to have a better defined photonic bandgap, the most appropriate number of periods of the alternating layers should be higher than ten and corresponds to a photonic bandgap of 1.60 eV. We have also theoretically reproduced the experimental transmission and reflection spectra with good agreement.