Electrically active defects in n-type 4H–silicon carbide grown in a vertical hot-wall reactor

Abstract

We have studied intrinsic and impurity related defects in silicon carbide (SiC) epilayers grown with fast epitaxy using chemical vapor deposition in a vertical hot-wall reactor. Using capacitance transient techniques, we have detected low concentrations of electron traps (denoted as Z1/2, EH6/7 and titanium) and hole traps (denoted as HS1 and shallow boron) in the n-type 4H–SiC epilayers. The concentration of intrinsic defects (Z1/2, EH6/7, and HS1 centers) increases with increasing growth temperature. The incorporation of shallow boron (B) decreases at higher growth temperatures, whereas the titanium (Ti) concentration is not sensitive to the growth temperature. The concentration of shallow B and Ti increases with increasing C/Si ratio. The concentration of the EH6/7 and the HS1 centers however, decreases with increasing C/Si ratio. We have also tested graphite susceptors with TaC or SiC coating and observed that the purity of the susceptor material plays a critical role in reducing the background impurity incorporation. The correlation with the carrier lifetime of these epilayers indicates that the EH6/7 and the Z1/2 centers may be the lifetime limiting defects in the investigated epilayers.

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

“…Peaks A and B with activation energy $0.2 eV can be produced by Al, B impurities, and complexes such as Al-related L-center with reported ionization energies 0.23 eV, (0.23-0.28 eV), and 0.24 eV above valence band edge, respectively. 13,14 Such an assignment complies with TSC studies of SI 4H-SiC (Ref. 10) where Al related trap with E a ¼ 0.22 eV was peaked at 105 K. We have tentatively assigned peak C at $242 K (E a ¼ 0.57 eV) to the Z 1/2 center.…”

“…10) where Al related trap with E a ¼ 0.22 eV was peaked at 105 K. We have tentatively assigned peak C at $242 K (E a ¼ 0.57 eV) to the Z 1/2 center. 10,13,14 Although the reported activation energy of Z 1/2 center (0.63-0.68 eV) and the typical peak temperature are somewhat higher than that for peak C, this is the only electron trap candidate for this peak that we were able to find in the published literature. Peak D matches with electron trap IL 1 (Ref.…”

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

“…These trap centers can be produced by the Al, B impurities, and L defect center, having close ionization energies of 0.23 eV (0.23-0.28 eV), and 0.24 eV above the valence band edge, respectively. 10,18 This correlation complies with the TSC studies of the SI 4H-SiC (Ref. 12) where the Al related trap with E a ¼ 0.22 eV was peaked at 105 K. The intensity of peak 3 was approximately the same at 0 V and at À5 V bias.…”

“…Intrinsic defects or complexes involving impurities and intrinsic defects have been reported in as-grown SiC epilayers. 9,10 However, their influence on the properties of the SiC epilayers is not well established and still less is known about their incorporation or formation behavior during the CVD process.…”

Influence of Growth Temperature on Carrier Lifetime in 4H-SiC Epilayers

“…Other ways to improve carrier lifetime is to minimize the deep level concentrations through optimization of growth conditions. Intrinsic defect concentrations have been studied as function of growth conditions [4,5], where low C/Si ratio and low growth temperature seem preferable for improving the carrier lifetime.…”