Deep Levels in As-Grown 4H-SiC Epitaxial Layers and their Correlation with CVD Parameters

Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by deep level transient spectroscopy in the as-grown state. Besides the Z1,2 defect level at EC- 0.66 eV, that seems to be omnipresent, four other electron traps labeled IL1 to IL4 with ionization energies between 0.87 and 1.31 eV could be detected. The dependence of the deep level concentrations on the incorporated N concentration ranging from few 1014 to some 1015 cm-3 and the C/Si ratio (1.2¸3) was examined. The concentration of both Z1,2 and IL1 increases with increa-sing N doping. For medium C/Si ratios this dependence is linear for Z1,2 and quadratic for IL1. High C/Si ratios enhance the formation of Z1,2 while they suppress that of IL1. These results suggest a complex of interstitial C and N on carbon site (Ci-NC) for Z1,2 and a nitrogen pair (NC-Ni) for IL1. However, other possibilities like Si vacancy related defects cannot be ruled out at present.