Influence of extended defects and oval shaped facet on the minority carrier lifetime distribution in as-grown 4H-SiC epilayers

Abstract The minority carrier lifetime distributions in 30 μm–190 μm thick 4H-SiC epilayers grown on 4 inch heavily nitrogen doped 4H-SiC substrates were measured by microwave photoconductive decay (μ-PCD) with a resolution of 1 mm lateral step, revealing three types of distribution patterns: a monotonous decrease in lifetime from the center to the edge (type 1), embedded with scattered regions in lower lifetime (type 2) or an oval shaped dark facet region in higher lifetime (type 3). Then, high resolution lifetime mapping measurements were further performed on these microareas with a lateral step size of 62.5 μm, which are compared with defects characterization results by Candela CS920 at the same position. It is found that the lifetime degradation correlates well with the stacking faults (SFs) and triangle defects. In general, the influence of triangle defect on lifetime degradation is more prominent than SF. In addition, surface roughness, lattice plane bending and crystal quality of oval shaped facet have been investigated by atomic force microscope (AFM) and high resolution X-ray diffraction (HRXRD). One possible reason for the higher lifetime over the oval shaped facet was proposed based on crystal quality and diffusion length.