  Electrical properties of point defects in 4$H$-SiC have been studied
extensively, but those related to carbon interstitials (C$_{i}$) have remained
surprisingly elusive until now. Indeed, when introduced via ion irradiation or
implantation, signatures related to C$_{i}$ observed by deep level transient
spectroscopy (DLTS) tend to overlap with those of other primary defects, making
the direct identification of C$_{i}$-related levels difficult. Recent
literature has suggested to assign the so-called M center, often found in
as-irradiated 4H-SiC, to charge state transitions of the C$_{i}$ defect in
different configurations. In this work, we have introduced excess carbon into
low-doped n-type 150 {\mu}m thick 4$H$-SiC epilayers by thermal annealing, with
a pyrolyzed carbon cap on the sample surface acting as a carbon source. Because
the layers exhibited initially low concentrations of carbon vacancies
([V$_{C}$] = 10$^{11}$ cm$^{-3}$), this enabled us to study the case of
complete V$_{C}$ annihilation, and formation of defects due to excess carbon,
i.e. carbon interstitials C$_{i}$ and their higher-order complexes. We report
on the occurrence of several new levels upon C injection which are likely
C$_{i}$-related. Their properties are different from those found for the M
center, which points towards a different structural identity of the detected
levels. This suggests the existence of a rich variety of C$_{i}$-related
defects. The study will also help generating new insights into the microscopic
process of V$_{C}$ annihilation during carbon injection processes.
