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 (10(9)-10(11) cm-2) of B-11 and Si-28 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 (E(c)) 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 E(c) - 0.18, E(c) - 0.23 and E(c) - 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 E(c) - 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 we 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 E(c) - 0.23 and E(c) - 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.