Impact of the end of range damage from low energy Ge preamorphizing implants on the thermal stability of shallow boron profiles Diffusion of B in Ge is studied in the temperature range 800-900°C using implantation doping and B doped epitaxial Ge layers. Concentration profiles before and after furnace annealing were obtained using high resolution secondary ion mass spectroscopy (SIMS). Diffusion coefficients were calculated by fitting the annealed profiles using TSUPREM. We obtained diffusivity values which are at least two orders of magnitude lower than the lowest values previously reported in the literature. Using our values an activation energy of 4.65͑±0.3͒ eV is calculated. Present experimental results suggest that interstitial mediated mechanism should be considered for B diffusion in Ge in accordance with recent theoretical calculations. Annealed SIMS profiles also suggest that B solid solubility in Ge is ϳ2 ϫ 10 18 cm −3 at 875°C which agrees with literature values.
The diffusion of boron (B) in germanium (Ge) is studied. B was introduced in Ge wafers by ion implantation, and concentration profiles after furnace annealing were obtained using secondary ion mass spectroscopy. The diffusion coefficient and solid solubility of B in Ge has been calculated to be 1.5(±0.3)×10−16 cm2/s and 5.5(±1.0)×1018/cm3, respectively, at 850 °C by fitting experimentally obtained profiles. This value of diffusion coefficient is at least two orders of magnitude lower than the minimum value reported in the literature for B diffusion in Ge. The results are significant as they question the general agreement about vacancy diffusion as the mechanism responsible for diffusion of B in Ge.
It is shown that strain relaxation during annealing of Si/GexSi1−x/Si heterostructures is significantly enhanced if the strained GexSi1−x layers are implanted with p (B) or n (As) type dopants below the amorphization dose. Comparison of strain relaxation during in situ annealing studies in a transmission electron microscope between unimplanted and implanted structures reveals that the latter show residual strains substantialy below those for unimplanted structures. We propose that this enhanced relaxation is caused by increased dislocation nucleation probabilities due to the high point-defect concentrations arising from implantation.
Most boron diffusion studies in Si–Ge have been made in regions of uniform germanium content. In this paper diffusion is observed from a boron-doped epitaxial silicon layer across surrounding Si–Ge layers. Pileup of boron in the Si–Ge layers shows that the activity coefficient for boron in Si–Ge is lower than that for pure silicon. A simple pairing model for Si–B interaction fitted the pileup quite well, with the same equilibrium constant applying to both Si0.9Ge0.1 and Si0.97Ge0.03 layers. The effect of this was simply to immobilize a significant fraction of the boron while retaining its acceptor qualities, the ratio of immobile boron to normal substitutional boron being proportional to the germanium content. Quasielectric field effects at the Si–SiGe interface have a strong effect on the results obtained.
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