Mapping of large structural defects in SiC Schottky contacts using internal photoemission microscopy

Abstract

4H–SiC and 6H–SiC epitaxial layers have been characterized by the scanning internal photoemission microscopy (SIPM) method based on use of Ni Schottky contacts. Geometrical patterns with widths of a few tens of microns were observed in the photoyield (Y) maps obtained for the 4H–SiC samples with a slightly lower Schottky barrier and a larger ideality factor than those in the current-voltage (I–V) characteristics; these patterns are caused by stacking faults located in the depletion region. SIPM also provided clear images of small particles adhered to the sample, which appeared as dark spots in the Y maps. These particles behaved as insulating materials and blocked the photocurrent flow; this behavior could not be detected from the conventional I–V characteristics. On the 6H–SiC samples, the violet SIPM measurements revealed surface pits, which originated from screw dislocations and were also shown as dark spots. We consider SIPM to be a powerful tool for investigation in inhomogeneities in crystal quality in conjunction with the electrical characteristics.