Tuning photonic crystal nanocavity modes by wet chemical digital etching

We have developed a wet chemical digital etching technique for tuning the resonant wavelengths of photonic crystal (PC) nanocavities over a wide range of $80\mathrm{nm}$ in precise $2–3\mathrm{nm}$ steps while preserving high cavity quality factors. In one tuning step, a few monolayers of material are removed from the cavity surface by etching a self-formed native oxide in $1\mathrm{mol}$ citric acid. Due to the self-limiting oxide thickness, total tuning range is based only on the number of etch steps, resulting in a highly controlled, digital tuning ability. We have characterized the tuning behavior of GaAs PC defect cavities of both square and triangular lattice symmetry and proven the effectiveness of this method by tuning a mode into resonance with the charged exciton, and then later the biexciton, transition of a single $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ self-assembled quantum dot.