In this paper, the impact of high-temperature annealing of 4H silicon carbide (SiC) on the formation of intrinsic defects, such as Z_[1/2] and EH_[6/7], and on carrier lifetimes was studied. Four nitrogen-doped epitaxial layers with various initial concentrations of the Z_[1/2]- and EH_[6/7]-centers (10^[11]-10^[14]cm^[-3]) were investigated by means of deep level transient spectroscopy and microwave photoconductance decay. It turned out that the high-temperature annealing leads to a monotone increase of the Z_[1/2]- and EH_[6/7]-concentration starting at temperatures between 1600℃ and 1750℃, depending on the initial defect concentration. In the case of samples with high initial defect concentration (10^[14]cm^[-3]) a distinct decrease in Z_[1/2]- and EH_[6/7]-concentration in the temperature range from 1600℃ to 1750℃ was observed, being consistent with previous reports. For higher annealing temperatures (Tanneal ≥ 1750 ∘C), the defect concentration is independent of the samples' initial values. As a consequence, beside the growth conditions, such as C/Si ratio, the thermal post-growth processing has a severe impact on carrier lifetimes, which are strongly reduced for samples annealed at high temperatures.
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