Lattice location and stability of implanted Cu in Ge

We report on emission channeling experiments using the radioactive isotope $^{67}$Cu implanted into single crystalline i-Ge at a dose of 2.4 $\times 10^{12}$ cm$^{-2}$. The lattice location of $^{67}$Cu was determined from the angular-dependent $\beta^{-}$ emission yield, which was measured by means of a position-sensitive detector around the <111>, <100> and <110> directions. We find that already in the as-implanted state a considerable fraction of Cu (20-25%) occupies ideal substitutional lattice positions, a similar fraction is located on positions that are displaced around 0.5-0.6 from substitutional sites. Following annealing at 300°C for 10 min, the substitutional fraction of implanted Cu increased to 45% while the fraction of displaced Cu decreased to 23%. Upon further annealing at 400°C, channeling effects disappeared completely and around 10% of $^{67}$Cu diffused out of the Ge sample. From this we can estimate the activation energy for dissociation of substitutional Cu to be around 1.6-1.9 eV.