A porous device for optical and electronic applications comprises a single crystal substrate and a porous single crystal structure epitaxially disposed on the substrate, where the porous single crystal structure includes a three-dimensional arrangement of pores. The three-dimensional arrangement may also be a periodic arrangement. A method of fabricating such a device includes forming a scaffold comprising interconnected elements on a single crystal substrate, where the interconnected elements are separated by voids. A first material is grown epitaxially on the substrate and into the voids. The scaffold is then removed to obtain a porous single crystal structure epitaxially disposed on the substrate, where the single crystal structure comprises the first material and includes pores defined by the interconnected elements of the scaffold.