High-Q photonic crystal cavities with embedded quantum dots

Defects in photonic crystals (PCs) can support localized light modes with extremely small mode volumes. Depending on the symmetry of the PC, and the means of fabrication of the PC, extremely high quality factors (Q) are also possible. The combination of high Q and small mode volume should allow us to observe strong coupling between the cavity and quantum dot (QD) emitters that are strategically embedded within the cavity. This, in turn, has important implications for a variety of optical phenomena, such as single-photon sources. We describe the fabrication of PCs formed within membranes (180 nm thick) of GaAs, of either triangular or square lattice symmetry. The structures incorporate InAs QDs, grown monolithically with the PC material by Molecular Beam Epitaxy (MBE). We have observed emission from the smallest volume cavities (i.e. single-hole defects) in both the triangular and square lattice structures. The cavities have lattice constants ranging from 0.25 – 0.40 μm, and Q factors as high as 8500. To improve the probability of coupling a single QD to a cavity mode, we have developed a lithographic positioning technique capable of aligning a cavity to a feature on the surface within 50 nm, adequate to overlap a QD with a cavity mode. We will report on the progress achieved thus far with these structures and the challenges remaining to achieve strong coupling with specific QDs.