Slow de-trapping of minority holes in n-type 4H-SiC epilayers



The carrier lifetime in epilayers of n-type 4H-SiC with low concentrations of the Z1/2 lifetime killer has been investigated over a wide range of temperature under low injection conditions. It was found that in addition to the primary initial decay dominated by surface recombination (SR), as determined by previous work, in some samples a slow decay component is observed, exhibiting a thermally activated recombination rate. Such a slow tail on the carrier decay can be of concern in high voltage switching devices. The slow decay was well accounted for by the thermal emission of minority carriers trapped on a defect. The resulting analysis has determined that the responsible trap is located ≈Ev + (0.37–0.58) eV with relatively small capture cross-sections for both electrons and holes: σp ≈ (0.5–12) × 10−17 cm2; σn < (0.3–8) × 10−18 cm2. Comparing these characteristics with reports in the literature for as-grown materials, the most likely candidates for the responsible defects are the D- and/or i-centers, which have similar ionization energies and capture cross-sections.