Two-photon-excited, three-dimensional photoluminescence imaging and dislocation-line analysis of threading dislocations in 4H-SiC

This paper describes the three-dimensional imaging of threading edge dislocations (<a>TEDs), pure c threading screw dislocations (<c>TSDs), and c + a threading mixed dislocations (<c + a>TMDs) in 4H silicon carbide (4H-SiC) epilayers by two-photon-excited photoluminescence (2PPL), where inclinations of dislocations in epilayers with different offcut angles are investigated. A numerical model based on carrier diffusion explains the mechanism of the dark-contrast 2PPL imaging provided by band edge emission. More than 450 threading dislocations in 4H-SiC epilayers are visualized three-dimensionally and are classified into six <a>-type TEDs, two <c>-type TSDs, and twelve <c + a>-type TMDs according to the directions of extra half-planes and the chiral geometries (right- or left-handed screw). The 2PPL images reveal that all threading dislocation types incline in the step-flow direction, the extent of which is more prominent for a larger offcut angle. The <a>TEDs also incline in the directions of their extra half-planes. The inclinations of <c>TSDs perpendicular to the step-flow direction are influenced by chirality, while those of <c + a>TMDs are influenced by both the directions of the extra half-planes and the chirality. The origins of the dislocation inclinations are discussed taking into account the kinetic interactions between the dislocations and the advancing steps on the growing surface.