METAL METAL EPITAXY ON GERMANIUM NEAR ROOM TEMPERATURES - NI(100)/CU(100)/GE(100)

(100) Cu films have been deposited on (100) Ge using electron-beam evaporation without intentional heating of the substrates, similar to the work using (100) Si substrates. Further deposition of Ni on the (100) Cu retains the (100) growth of Ni also, thus allowing metal-metal epitaxy on germanium. The thermal stability of the (100) Ni/Cu/Ge(100) is studied, and compared with that of the (100) Ni/Cu/Si(100). The Cu-Ge reaction starts around 150-degrees-C, lower than the Cu-Si one. The Ni-Ge reaction is observed between 200 and 250-degrees-C, also at temperatures lower than that of Ni-Si. The Cu (100) lattice is found to rotate by 45-degrees around its (001) axis relative to the Ge (100) plane. This is shown to be needed for such an epitaxial growth to occur, similar to that observed for the (100) Cu/Si structure. The possible fabrication of both the metallic and device structures on a GaAs substrate is discussed, using the Ge layer epitaxially grown on GaAs for the metal growth.