Single Shockley faults (SSF) have been studied in 4H-SiC epitaxial layers by using a spatial resolved micro-photoluminescence technique. In particular the effect of the UV pumping laser has been investigated. Samples have been irradiated at different power densities in order to find a threshold for the growth of the SSF defects. A low power density (115 W/cm2) exposition at 325 nm does not affect the structural properties of the epitaxial layers. We observed a growth of this defect through the epitaxial layers when the power density is increased over the value of 115 W/cm2.