Silicon–Germanium: The Legacy Lives On

Alloy systems comprised of silicon with germanium, lead tellurium, and bismuth antimony have constituted a majority thermoelectric applications during the last half-century. These legacy materials are primarily covalently bonded maximum ZT near one. Silicon–germanium alloys provided thermal to electrical conversion for many NASA’s radioisotope generator (RTG) configurations nearly all its deep space outer planetary flights, such as Pioneer I II, Voyager 11, Ulysses, Galileo, Cassini. The remarkable success these their respective devices is evidenced by fact that there has never been failure RTG even after over 1 billion cumulative mission-hours. history this alloy system material spans six decades research further improve performance continues day. Si-Ge long mainstay because fortuitous combination sufficiently high melting temperature, reasonable energy band gap, solubility both n- p-type dopants, exhibits complete miscibility in solid state, which enable tuning properties. This article reviews silicon–germanium use programs. Since device technology also critical operational consideration, brief review some unique challenges imposed an discussed.