Elimination of carbon vacancies in 4H-SiC epi-layers by near-surface ion implantation : Influence of the ion species

• The carbon vacancy (VC) is a prevailing point defect in high-purity 4H-SiC epitaxial layers, and it plays a decisive role in controlling the charge carrier lifetime. One concept of reducing the VC-concentration is based on carbon self-ion implantation in a near surface layer followed by thermal annealing. This leads to injection of carbon interstitials (Ci's) and annihilation of VC's in the epi-layer "bulk". Here, we show that the excess of C atoms introduced by the self-ion implantation plays a negligible role in the VC annihilation. Actually, employing normalized implantation conditions with respect to displaced C atoms, other heavier ions like Al and Si are found to be more efficient in annihilating VC's. Concentrations of VC below ∼2 × 1011 cm-3 can be reached already after annealing at 1400 °C, as monitored by deep-level transient spectroscopy. This corresponds to a reduction in the VC-concentration by about a factor of 40 relative to the as-grown state of the epi-layers studied. The negligible role of the implanted species itself can be understood from simulation results showing that the concentration of displaced C atoms exceeds the concentration of implanted species by two to three orders of magnitude. The higher efficiency for Al and Si ions is attributed to the generation of collision cascades with a sufficiently high energy density to promote Ci-clustering and reduce dynamic defect annealing. These Ci-related clusters will subsequently dissolve during the post-implant annealing giving rise to enhanced Ci injection. However, at annealing temperatures above 1500 °C, thermodynamic equilibrium conditions start to apply for the VC-concentration, which limit the net effect of the Ci injection, and a competition between the two processes occurs.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

Aluminum

Annealing

Atoms

Bandwidth

Carrier lifetime

Deep level transient spectroscopy

Defect density

Ion implantation

Point defects

Silicon carbide

Vacancies

Annealing temperatures

High energy densities

Implantation conditions

Near-surface layers

Post-implant annealing

Self-ion implantation

Thermodynamic equilibria

Three orders of magnitude

Ions

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