Silicon Nanobeam Cavities
Work towards finding high quality factor (Q) cavities led to the study of silicon 1D photonic crystal nanobeam cavities due to their experimentally measured Q of ≈100,000 for unsuspended cavities (compared to the typical ≈10,000-20,000 for GaAs based 2D photonic crystals). These cavities can be measured using a small radius fiber taper loop or by using cross polarized resonant scattering (http://dx.doi.org/10.1364/OE.18.020558).
Using atomic layer deposition (ALD) to coat the cavity with Al2O3 the Q can be increased to over 200,000 with an increase of 38% on average (http://dx.doi.org/10.1364/JOSAB.29.000A55). This increase in Q is mostly attributed to decreased surface roughness due to the conformal nature of ALD and to surface passivation which leads to decreased absorption by surface states. These are still empty cavities without any active emitters. Some possible ways to incorporate active emitters while still taking advantage of the high Q due to the silicon processing would be doping the ALD coating with active rare earth elements or through III-V/silicon integration.