The diffusivity of Cu impurity was studied in amorphous samples which had been prepared by MeV Si implantation. The 0.0022mm-thick layers were first annealed at 500C and then implanted with 200keV Cu ions, which restored a 300nm-thick surface layer to the as-implanted state. The Cu concentration profiles were measured by using 4He back-scattering. After diffusion at temperatures of between 150 and 270C (table 34), solution partitioning was detected at sharp phase boundaries between the annealed and Cu-implanted layers. The partition coefficient could be as high as 8. The diffusion coefficient in annealed amorphous material was 2 to 5 times larger than that in as-implanted amorphous material. The activation energies were 1.39 and 1.25eV, respectively. Defects played an important role.

Defect States of Amorphous Si Probed by the Diffusion and Solubility of Cu. A.Polman, D.C.Jacobson, S.Coffa, J.M.Poate, S.Roorda, W.C.Sinke: Applied Physics Letters, 1990, 57[12], 1230-2

Table 34

Diffusivity of Cu in Amorphous Si