Suppression of segregation of the phosphorus ?-doping layer in germanium by incorporation of carbon

The successful formation of abrupt phosphorus (P) ?-doping profiles in germanium (Ge) is reported. When the P ?-doping layers were grown by molecular beam epitaxy (MBE) directly on Ge wafers whose surfaces had residual carbon impurities, more than a half the phosphorus atoms were confined successfully within a few nm of the initial doping position even after the growth of Ge capping layers on the top. On the other hand, the same P layers grown on Ge buffer layers that had much less carbon showed significantly broadened P concentration profiles. Current-voltage characteristics of Au/Ti/Ge capping/P ?-doping/n-Ge structures having the abrupt P ?-doping layers with carbon assistance showed excellent ohmic behaviors when P doses were higher than 1×1014cm%2 and the capping layer thickness was as thin as 5 nm. Therefore, the insertion of carbon around the P doping layer is a useful way of realizing ultrashallow junctions in Ge.