We have introduced a photonic crystal into a single-crystal silicon slab in order to manipulate the light emission. When the lattice constant of a defect-free photonic crystal matches the wavelength of light in the medium, the light emitted from the silicon is resonantly extracted at the photonic band edge within the escape light cone. When the lattice constant is larger than the wavelength, Brillouin zone folding of the photonic band also allows the light to be extracted; we achieved an intensity that was enhanced by a factor of $sim$20 due to the diffraction of internal light into the light cone. We have also created a point defect in photonic crystals with smaller lattice constants that functions as a nanocavity and strongly interacts with the silicon emitter. Four cavity modes were observed, with different $Q$ -factors and emission patterns. The mode orders were assigned using the resonant wavelengths and polarizations. The observed emission at room temperature was enhanced by a factor of $sim$30 in comparison to that of an unprocessed area of silicon-on-insulator. Our study demonstrates that employing a photonic crystal nanocavity in silicon can greatly improve the light extraction efficiency, the characteristics of the radiation pattern, and the internal quantum efficiency.
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