Formation of carbon interstitial-related defect levels by thermal injection of carbon into n-type 4H-SiC

Abstract

Electrical properties of point defects in 4H-SiC have been studied extensively, but those related to carbon interstitials (Ci) have remained elusive until now. Indeed, when introduced via ion irradiation or implantation, signatures related to Ci observed by deep level transient spectroscopy tend to overlap with those of other primary defects, making the direct identification of Ci-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 Ci defect in different configurations. In this work, we have introduced excess carbon into low-doped n-type 150 μm thick 4H-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 ([VC]=1011cm), this enabled us to study the case of complete VC annihilation and formation of defects due to excess carbon, i.e., carbon interstitials Ci and their higher-order complexes. We report on the occurrence of several new levels upon C injection, which are likely Ci-related. Their properties are different from those found for the M center, which point toward a different microscopic identity of the detected levels. This suggests the existence of a rich variety of Ci-related defects. The study will also help generating new insights into the microscopic process of VC annihilation during carbon injection processes.