In this paper, we demonstrate how to efficiently control the quality factor of silicon nitride nanobeam cavities, grown on a silica substrate and embedded in an upper cladding, by engineering the nanobeam cross-section and the shape of the periodic holes. We propose optimized configurations that are able to overcome the decreasing of the Q-factor when the nanobeam is embedded in an asymmetric medium. More precisely, we show that the maximum achievable quality factor can be designed and tuned in

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... asymmetric configurations where the upper cladding is particularly different from the substrate one. These optimized configurations exhibit high-Q factor and small mode volume over a wide range of the upper cladding refractive index paving the way for the realization of innovative optical sensors and for the compensation of fabrication tolerances in embedded optical nanobeam cavities.