Implantation of sodium ions into germanium

The donor properties of Na atoms introduced by ion implantation into $p$-Ge with the resistivity 20–40 $\Omega$ cm are established for the first time. Na profiles implanted into Ge (the energies 70 and 77 keV and the doses (0.8, 3, 30) $\times$ 10$^{14}$ cm$^{-2}$) are studied. The doses and annealing temperatures at which the thermoprobe detects $n$-type conductivity on the sample surface are established. After implantation, the profiles exhibit an extended tail. The depth of the concentration maximum is in good agreement with the calculated mean projected range of Na ions $R_p$. Annealing for 30 min at temperatures of 250–700$^\circ$C brings about a redistribution of Na atoms with the formation of segregation peaks at a depth, which is dependent on the ion dose, and is accompanied by the diffusion of Na atoms to the surface with subsequent evaporation. After annealing at 700$^\circ$C less than 7% of the implanted ions remain in the matrix. The shape of the profile tail portions measured after annealing at temperatures 300–400$^\circ$C is indicative of the diffusion of a small fraction of Na atoms into the depth of the sample.