As-grown 4H-SiC epitaxial layers were investigated by means of deep-level transient spectroscopy in order to study the formation of the well-known Z1,2 defect, with energy levels that were normally detected at about EC–0.7eV. Chemical vapor deposition, and various N-doping concentrations and C/Si ratios (1.2 to 3) in the gas phase, were used to prepare the samples. The Z1,2 defect concentration was observed to increase with the incorporated N concentration. The dependence was linear for medium C/Si ratios (1.5 to 2.5). The highest and lowest applied C/Si ratios (3 and 1.2) enhanced and suppressed the Z1,2 defect formation, respectively. This behavior suggested a complex of N with interstitial C atoms or, less probably, Si vacancies. In particular, a correlation between Z1,2 defect formation and N incorporation was clearly shown; contrary to previous conclusions. Previously reported negative-U properties of the Z1,2 deep-level defects were confirmed. A 1:1 relationship between the concentrations of Z1 and Z2 was obtained in the present as-grown epitaxial layers.

Formation of the Z1,2 Deep-Level Defects in 4H-SiC Epitaxial Layers - Evidence for Nitrogen Participation. I.Pintilie, L.Pintilie, K.Irmscher, B.Thomas: Applied Physics Letters, 2002, 81[25], 4841-3