We propose the development of nanoscale superlattices (SLs) as the active elements of high efficiency thermoelectric coolers. Recent models predict that the thermoelectric figure of merit ZT can reach 4 for elements fabricated from HgCdTe-based SLs and could exceed 6 for related metal/semiconductor SLs. The feasibility of using HgCdTe and metal-based SL materials with embedded nanodefects for increased hot-carrier transport during thermoelectric cooling will be demonstrated in the proposed Phase 1 effort. We will perform calculations to optimize the material parameters of HgCdTe- and metal-based SL structures to maximize ZT. Next, we will use our extensive experience in molecular beam epitaxy to grow the designed structures. Finally, we will develop device structures and metallization methods appropriate for performing ZT measurements, measure the ZTs of fabricated devices and compare results with theory.