  We provide direct evidence that the broad Z$_{1/2}$ peak, commonly observed
by conventional DLTS in as-grown and at high concentrations in radiation
damaged $4H$-SiC, has two components, namely Z$_{1}$ and Z$_{2}$, with
activation energies for electron emission of 0.59 and 0.67~eV, respectively. We
assign these components to
$\mathrm{Z}_{1/2}^{=}\rightarrow\mathrm{Z}_{1/2}^{-}+e^{-}\rightarrow\mathrm{Z}_{1/2}^{0}+2e^{-}$
transition sequences from negative-$U$ ordered acceptor levels of carbon
vacancy (V$_{\mathrm{C}}$) defects at hexagonal/pseudo-cubic sites,
respectively. By employing short filling pulses at lower temperatures, we were
able to characterize the first acceptor level of V$_{\mathrm{C}}$ on both
sub-lattice sites. Activation energies for electron emission of 0.48 and
0.41~eV were determined for $\mathrm{Z}_{1}(-/0)$ and $\mathrm{Z}_{2}(-/0)$
transitions, respectively. Based on trap filling kinetics and capture barrier
calculations, we investigated the two-step transitions from neutral to doubly
negatively charged Z$_{1}$ and Z$_{2}$. Positions of the first and second
acceptor levels of V$_{\mathrm{C}}$ at both lattice sites, as well as $(=\!/0)$
occupancy levels were derived from the analysis of the emission and capture
data.
