In this work, it is revealed that the well-known S1 defect level, assigned to the Si vacancy (VSi) in 4H-SiC [1], consists of up to three contributions, two of which are related to carbon antisite-vacancy (CAV) pair structures. The defects were identified by consistent defect characteristics, namely the trap level EC − ET with respect to the conduction band bottom (EC being the energy of the conduction band edge), the capture cross-section σ , determined by admittance spectroscopy (AS), and hybrid density functional theory (DFT) calculations. High-resolution AS was used to analyze intrinsic electrically active defects in various 4H-SiC samples. For comparison of characteristics and identification of the underlying defects, deep-level transient spectroscopy (DLTS) and, complementary, DFT calculations were performed. Differently grown, non-commercial 4H-SiC samples of type A, B, and C with Schottky contacts based on specific growth parameters were selected (see Ref. [2] for growth parameters and Fig. 1 (b) for doping concentrations ND). While the epi(taxial)-layers of type A and B were (0001) oriented and grown 4° off-cut towards the [11 ̄20] direction, sample type C was grown on-axis along the [11 ̄20] direction. Additionally, commercial 1.2 kV Schottky diodes purchased from CREE / Wolfspeed were analyzed (sample type D). Fig. 1 (a) shows an example of a conductance spectrum for sample type B. The maxima of the conductance at the different temperatures follow Arrhenius behavior, allowing to calculate the trap level EC − ET, the capture cross-section σ , and the defect density Nt of the trap. The defect characteristics measured by AS and DLTS are summarized and compared in Fig. 1 (b). Clearly, the σ and EC − ET of Z1/2 is quite well comparable between the two measurement techniques. However, significant differences between the results from AS and DLTS, especially in the capture cross section, are found for the level assigned to S1. The S1 defect was also detected in sample type D. In order to further investigate its details, one sample was exposed to a 1.8 MeV proton beam of 1 × 1012 cm−2 fluence at an angle of 8◦ with respect to the surface normal to avoid channeling. In Fig. 2, two frequency and temperature dependent conductance peaks (cf. Peak I and III) are clearly visible at −1 V DC bias for the (a) non-irradiated and (b) irradiated sample. A shoulder between both peaks of the non-irradiated sample (cf. Peak II), which becomes distinct after the irradiation, indicates a third contribution. Using the conductance maxima, the defect characteristics of all three contributions are found to be in the range of the literature values for S1. [3] The relatively small capture cross-section of Peak III indicates a low probability of capturing another electron (the majority charge carrier in n-type SiC) into this defect configuration. Therefore, an assignation to the triple-negatively charged silicon vacancy is reasonable. For Peak I and II, the σ has been determined to be about 3 orders of magnitude larger than for Peak III. Here, the probability of capturing or releasing another electron is higher. Peaks I and II are, therefore, considered to be contributions from CAV-type of defects, as their transitions are anticipated to involve the neutral state [4]. From hybrid DFT studies we found that CAV and VSi defect configurations are separated by high energy barriers (> 3 eV), which could explain the formation of both structures under growth (non-equilibrium) conditions [4]. Besides calculating formation energies and charge transition levels of CAV and VSi, the carrier capture kinetics was investigated from first-principles. Here, we calculated the coefficients and cross-sections for the capture of free-electrons at CAV and VSi traps [5]. Table 1 collects the defect characteristics for both, AS measurements and hybrid DFT calculations. While the results support the hypotheses provided above, a deeper analysis is presented in the final paper.