Tuning of photonic crystal band properties by atomic layer deposition

We report the application of atomic layer deposition to manipulate the dielectric architecture of conventional and superlattice two-dimensional photonic crystal waveguides fabricated in silicon. Conformal deposition of a second dielectric layer is shown to have a dramatic influence on the photonic band structure and produces unique effects that cannot be emulated in a single dielectric slab photonic crystal material. With additional dielectric coatings, a strong decrease in photonic band frequencies and change in band slope are observed, which for the lowest photonic states produces strong degeneracies. The capability, in principle, to tune the position of bands to within 0.005% accuracy, is demonstrated. Additionally, new features are observed when differential band shifts result in band-crossing and for which like polarizations activate perturbation mechanisms that result in local and strong band curvatures. The extremely strong band bending resulting from band-band interactions could have applications, in slow light devices, and provide a way to introduce non-linear effects into tunable photonic crystal structures.