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 nitrogendoped epitaxial layers with various initial concentrations of the Z 1=2-and EH 6=7-centers (10 11 À 10 14 cm À3) 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 C and 1750 C, depending on the initial defect concentration. In the case of samples with high initial defect concentration (10 14 cm À3) a distinct decrease in Z 1=2-and EH 6=7-concentration in the temperature range from 1600 C to 1750 C was observed, being consistent with previous reports. For higher annealing temperatures (T anneal ! 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 postgrowth processing has a severe impact on carrier lifetimes, which are strongly reduced for samples annealed at high temperatures. V

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Lifetime measurements are performed on 4H-SiC pin power diodes (6.5 kV). The lifetime values in the base range from 1.1 s to 2.1 s; these values demonstrate the high quality of the 4H-SiC epilayer and the optimized device processing. The observed lifetimes are correlated with deep defect centers detected by deep level transient spectroscopy. The role of the Z1/2-center as a lifetime killer is discussed.

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Deep Level Transient Spectroscopy (DLTS) and Double-correlated DLTS (DDLTS) measurements have been conducted on Schottky contacts fabricated on n-type 4H-SiC epilayers using different contact metals in order to separate the EH6- and EH7-centers, which usually appear as a broad double peak in DLTS spectra. The activation energy of EH6(EC- ET(EH6) = 1.203 eV) turns out to be independent of the electric field. As a consequence, EH6is acceptor-like according to the missing Poole-Frenkel effect. Therefore, it can be excluded that the EH6-center and the prominent acceptor-like Z1/2-center belong to different charge states of the same microscopic defect as theoretically suggested. It is proposed that EH6is a complex containing a carbon vacancy and another component available at high concentrations. The activation energy of EH7(EC- ET(EH7) = 1.58 eV) has been evaluated indirectly by fitting the DLTS spectra of the EH6/7double peak taking the previously determined parameters of EH6into account.

Fe-implanted n-/p-type 4H-SiC samples were investigated by deep level transient spectroscopy (DLTS). In order to be able to separate Fe-related defect centers from defects caused by implantation damage, a corresponding Ar-profile was implanted. No Fe-related defects were observed in n-type 4H-SiC, while two Fe-related centers could be identified in p-type 4H-SiC. The electrical behavior of these centers is donor-like.

Two electrical measurement techniques are frequently employed for the characteri- zation of traps at the SiO2/SiC interface: the thermal dielectric relaxation current (TDRC) and the conductance method (CM). When plotting Dit as a function of the energy position Eit in the bandgap both techniques reveal comparable results for deep interface traps (EC􀀀Eit > 0:3 eV). For shallower traps, CM always shows a strong increase of Dit which originates from near interface traps (NIT). TDRC provides a contradictory result, namely a slight decrease of Dit. In this paper, we show that the position of NITs in the oxide close to the interface is responsible for the invisibility of these traps in TDRC spectra. We further show that NITs become detectable by the TDRC method by using a discharging voltage Vdis close to the accumulation regime. However, due to the Shockley-Ramo-Theorem the contribution of NITs to the Dit in TDRC spectra is strongly suppressed and can be increased by using thin oxides.