Deep levels in as-grown p-type 4H-SiC epilayers have been investigated by DLTS. Three
deep hole traps (HK2, HK3 and HK4) can be detected by DLTS in the temperature range from 350K
to 700K. They are energetically located at 0.84 eV (HK2), 1.27 eV (HK3) and 1.44 eV (HK4) above
the valence band edge. The activation energy of the traps does not show any meaningful change
regardless of applied electric field, indicating that the charge state of the deep hole traps may be
neutral after hole emission (donor-like). By the low-energy electron irradiation, the HK3 and HK4
concentrations are significantly increased, suggesting that the origins of the HK3 and HK4 may be
related to carbon displacement. Study on the thermal stability of these hole traps has revealed that the
trap concentrations of HK3 and HK4 are reduced to below the detection limit (1-2 × 1011 cm-3) by
annealing at 1350°C. The HK2 is thermally more stable than HK3 and HK4, and becomes lower than
the detection limit by annealing at 1550°C.