Gettering of Luminescent Point Defects along Step Bunching in 4H-SiC Epitaxial Layers by Ultraviolet Excitation

Abstract

Luminescent lines, perpendicular to the step flow direction, were observed in SiC epitaxial layers with ultraviolet (UV) excitation of the sample surface. These lines appear at step bunching sites in SiC epilayers with UV illumination of greater than 3 s at 50 W/cm2. They become brighter and wider, reaching a width of ∼5 μm. Zygo profilometry shows that there is a shallow triangular-shaped valley at the surface to the left of the luminescent lines, with reference to the step flow direction. The left apex of the valley starts at a local defect that is created during the epitaxial growth, and the valley fans out during subsequent epitaxial growth. The luminescent lines are at the right-side boundary of the triangle. Atomic force microscopy (AFM) profilometry shows that at this boundary there is a double macrostep at the sample surface, which is between 2.5 nm and 8 nm high. This relates to 5 to 15 bilayer steps. The first step is always observed to be smaller than the second one. There is a valley approximately 4 nm to 8 nm deep between them. The luminescent lines appear due to UV-activated diffusion and gettering of point defects to the double macrostep.