Abstract: A structure of periodically varying density is provided, that acts as a phonon resonator for phonons capable of participating in phonon-electron interactions. Specifically, a phonon resonator that is resonant for phonons of appropriate momentum to participate in indirect radiative transitions and/or inter zone intervalley scattering events is provided. Preferably, the structure is an isotope superlattice, most preferably of silicon. The structure of the present invention has improved optical, electrical, and/or heat transfer properties. A method of preparing a the structure of the present invention is also provided.