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

Abstract

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 Z 1,2 defect level at E C -0.66 eV, that seems to be omnipresent, four other electron traps labeled IL 1 to IL 4 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 10 14 to some 10 15 cm -3 and the C/Si ratio (1.2¸3) was examined. The concentration of both Z 1,2 and IL 1 increases with increasing N doping. For medium C/Si ratios this dependence is linear for Z 1,2 and quadratic for IL 1 . High C/Si ratios enhance the formation of Z 1,2 while they suppress that of IL 1 . These results suggest a complex of interstitial C and N on carbon site (C i -N C ) for Z 1,2 and a nitrogen pair (N C -N i ) for IL 1 . However, other possibilities like Si vacancy related defects cannot be ruled out at present.

Temperature dependence of current conduction in semi-insulating 4H-SiC epitaxial layer

“…Peak D matches with electron trap IL 1 (Ref. 15) at (E C À 0.87 eV) and capture cross-section $1 Â 10 À14 cm 2 , which are fairly close to that found from our TSC measurements. It is suggested that a complex involving two nitrogen atoms (N C -N i ) or a split interstitial on C site (N-N) C produce IL 1 center although V C , Si C , or Si i related defects are also a possibility.…”

“…The high peaking temperature of E center implies its high activation energy possibly close to the middle of the band gap. The trap centers with activation energies close to the middle of the bandgap were reported for as grown 4H-SiC epitaxial layers 15,16 and bulk SI 4H-SiC (Refs. 8, 17, and 18) and were attributed to intrinsic defects and their complexes.…”

“…It is suggested that a complex involving two nitrogen atoms (N C -N i ) or a split interstitial on C site (N-N) C produce IL 1 center although V C , Si C , or Si i related defects are also a possibility. 15 Further investigation is required to find the activation energy and capture cross section of the trap centers associated with feature E since its peak was swamped by high stray current. The high peaking temperature of E center implies its high activation energy possibly close to the middle of the band gap.…”

Characterization of deep levels in n-type and semi-insulating 4H-SiC epitaxial layers by thermally stimulated current spectroscopy

“…The candidates for this peak are electron trap, IL 2 , that was found in the 4 H-SiC epitaxial layers grown at low C/Si (Ref. 22) and defects SI-6 and SI-8 detected by electron paramagnetic resonance in high purity SI 4H-SiC. 23 The 1.1 eV center was also found in our TSC studies of bulk SI 4 H-SiC and was related either to V-complexes or intrinsic defects.…”

“…It is suggested that a complex involving two nitrogen atoms (N C -N i ) or a split interstitial on the C site (N-N) C produce an IL 1 center, although V C , Si C , or Si i related defects are also a possibility. 22 Further investigation is required to find the activation energy and capture cross section of the trap centers associated with feature E containing multiple peaks. Its highest intensity peak was swamped by a high stray current, associated with the thermoelectric effects.…”