Point defects in n-type silicon implanted with low doses of MeV boron and silicon ions
Czochralski-grown (cz) silicon samples have been implanted at room temperature with low doses (109-1011 cm-2) of 11B and 28Si using energies between 0.38 and 3.0 MeV. Deep-level transient spectroscopy has been applied for sample analysis, and four levels approximately 0.18, approximately 0.23, approximately 0.35 and approximately 0.43 eV below the conduction band edge (Ec) are resolved. The concentrations of these levels have been determined as a function of ion dose and sample depth. The total concentration of electrically active defects amounts to less than 10% of the vacancy concentration predicted by Monte Carlo simulations. The depth profiles of the levels at Ec-0.18, Ec-0.23 and Ec-0.43 eV are mainly confined to the damage peak region, and evidence is obtained for substantial surface-enhanced annihilation of migrating monovacancies. However, the depth distribution of the Ec-0.35 eV level exhibits a pronounced leading surface tail and is broader than expected from energy deposition calculations. The identity of this latter level is not well established but the authors' argue that the generation process involves diffusion of interstitial carbon. Finally, in contrast to that for cz samples irradiated with MeV electrons the strengths of the Ec-0.23 and Ec-0.43 eV levels deviate from a one-to-one proportionality. Similar deviations have previously been observed in ion-implanted float-zone samples and are attributed to strain accommodated by the lattice in the damage peak region.