Oxidation-enhanced annealing of implantation-induced Z1/2 centers in 4H-SiC: Reaction kinetics and modeling

High-purity epitaxial layers of n-type 4H-SiC have been implanted with 4.3-MeV Si ions to a dose of 3 x 10(8) cm(-2) and then subjected to dry isothermal oxidation at temperatures between 1050 and 1175 degrees C. Analysis of the samples by depth-resolved deep level transient spectroscopy unveils a strong oxidation-enhanced annealing of the prominent Z(1/2) center, commonly ascribed to the carbon vacancy. The integrated (total) loss of Z(1/2) centers is proportional to the thickness of the silicon dioxide (SiO2) layer grown but the proportionality constant, or annihilation efficiency, decreases with decreasing oxidation temperature. At a given depth x, the annealing of Z(1/2) obeys first-order kinetics with a rate constant c having an activation energy of similar to 5.3 eV. The pre-exponential factor c decreases with increasing x and a normalized concentration-versus-depth distribution of the species injected from the surface and annihilating the Z(1/2) centers has been deducted. This species is believed to be the carbon interstitial and is labeled C-I: numerical simulations of the reaction kinetics employing a model where (i) the generation rate of C-I at the SiO2/SiC interface is related to the oxidation rate, (ii) the diffusion of C-I into the SiC layer is fast, and (iii) a steady-state concentration profile of C-I is rapidly established, yield good agreement with the experimental data for the evolution of both Z(1/2) (absolute values) and C-I (relative values) with temperature, depth, and time. The activation energy obtained for the diffusivity of C-I is similar to 3.0 eV, presumably reflecting the migration barrier for C-I and possibly some contribution from an extra barrier to be surmounted at the SiO2/SiC interface.