Abstract: Forming a thermoelectric device may include forming a thermoelectric superlattice including a plurality of alternating layers of different thermoelectric materials wherein a period of the alternating layers varies over a thickness of the superlattice. More particularly, forming the superlattice may include depositing the superlattice on a single crystal substrate using epitaxial deposition. In addition, the single crystal substrate may be removed from the superlattice, and a second thermoelectric superlattice may be provided with the first and second thermoelectric superlattices having opposite conductivity types. Moreover, the first and second thermoelectric superlattices may be thermally coupled in parallel between two thermally conductive plates while electrically coupling the first and second thermoelectric superlattices in series. Related materials and devices and structures are also discussed.