Radiation-induced interstitial carbon atom in silicon: Effect of charge state on annealing characteristics

We present experimental and theoretical results showing that the migration of interstitial carbon atom (Ci) in silicon depends on its charge state. The experimental results were obtained from the analysis of changes in concentrations of the Ci defect, which were determined from deep level transient spectra, in n+-p diodes subjected to irradiation with 4-6 MeV electrons or α-particles at T ≤ 273 K and subsequent heattreatments in the temperature range 280-330 K with applied reverse bias voltage and without it. It has been found that in the positive charge state the Ci migration energy is 0.880.02 eV, while in the neutral charge state it is reduced to 0.73-0.74 eV. First-principles density-functional calculations of the structure of Ci in different charge states (z = 0, +1, -1) and diffusion coefficient parameters (activation barrier ΔEa and pre-exponential factor D0) have been performed. It has been found that a split-<100 > configuration with C2v symmetry is the most stable one for Ci in all the charge states. The following ΔEa and D0 values have been derived from the calculations: ΔEa = 0.74 eV and D0 = 0.06 cm2s-1 for Ci0, and ΔEa = 0.89 eV for Ci+.