Various aspects of the present invention are directed to photonic devices, such as electro-optic modulators, passive filters, and tunable filters. In one aspect of the present invention, a photonic device includes a semiconductor structure having a p-region and an n-region. A doped region is formed on or within the semiconductor structure. The doped region includes at least one generally periodic array of recesses, with the at least one generally periodic array configured to transmit electromagnetic radiation at a selected dominant wavelength. The selected dominant wavelength is tunable by varying the refractive index of the semiconductor structure.