Diffusion and recrystallization of B implanted in crystalline and pre-amorphized Ge in the presence of F

Although the diffusion control and dopant activation of Ge p-type junctions are straightforward when using B⁺ implantation, the use of the heavier BF₂⁺ ions or even BF⁺ is still favored in terms of shallow junction formation and throughput - because implants can be done at higher energies, which can give higher beam currents and beam stability - and thus the understanding of the effect of F co-doping becomes important. In this work, we have investigated diffusion and end-of-range (EOR) defect formation for B⁺, BF⁺, and BF₂⁺ implants in crystalline and pre-amorphized Ge, employing rapid thermal annealing at 600 °C and 800 °C for 10 s. It is demonstrated that the diffusion of B is strongly influenced by the temperature, the presence of F, and the depth of amorphous/crystalline interface. The B and F diffusion profiles suggest the formation of B-F complexes and enhanced diffusion by interaction with point defects. In addition, the strong chemical effect of F is found only for B in Ge, while such an effect is vanishingly small for samples implanted with F alone, or co-implanted with P and F, as evidenced by the high residual F concentration in the B-doped samples after annealing. After 600 °C annealing for 10 s, interstitial-induced compressive strain was still observed in the EOR region for the sample implanted with BF⁺, as measured by X-ray diffraction. Further analysis by cross-sectional transmission electron microscopy showed that the {311} interstitial clusters are the majority type of EOR defects. The impact of these {311} defects on the electrical performance of Ge p⁺/n junctions formed by BF⁺ implantation was evaluated.