PHASE FORMATIONS IN THE COPPER-GERMANIUM SYSTEM - REACTIONS, STRUCTURES AND RESISTIVITIES

The reaction of germanium with copper begins with the formation of the monoclinic Cu3Ge at temperatures as low as 125 degrees C. At approximately 200 degrees C, Cu3Ge reacts with excess copper to form a copper-rich phase, zeta, with a hexagonal close-packed structure. These results are compared with similar ones obtained with copper-silicon samples. The resistivity of zeta, measured as 47 mu Omega.cm for a germanium content of 15 at%, is compared to that which is calculated from the specific resistivity of germanium in copper. If sufficient amounts of copper are present the last process to happen is the dissolution of zeta into the remaining copper to form a solid solution: to be quite precise, the formation of the solid solution can already be found simultaneously with the formation of zeta. Marker experiments reveal that Cu3Ge forms by the motion of copper atoms, while zeta. forms by the motions of both copper and germanium in nearly equal proportions. Experiments, where Cu3Ge was prepared next to silicon, show that silicon atoms (and consequently those of germanium also) become mobile in Cu3Ge at a temperature considerably higher than required for the mobility of copper, namely about 250 degrees C versus 125 degrees C. In the presence of silicon Cu3Ge ceases to be stable at 300 degrees C.