Deep level transient spectroscopy on as-grown and electron-irradiated p-type 4H-SiC epilayers

The authors have investigated deep levels in as-grown and electron-irradiated $p$ -type 4H-SiC epilayers by deep level transient spectroscopy. In as-grown epilayers, the D center and four deep levels are observed. In $p$ -type 4H-SiC, reactive ion etching followed by thermal treatment (at 1150 °C) induces the HK0 $\left(E_V+0.79\text{eV}\right)$ and HK2 $\left(E_V+0.84\text{eV}\right)$ centers. By the electron irradiation, two deep levels at 0.98 eV (EP1) and 1.44 eV (EP2) are observed in all the samples irradiated at 116–400 keV, while two additional deep levels (EP3 and EP4) are observed only in the samples irradiated at 400 keV. After annealing at 950 °C, these centers are annealed out, and the HK4 $\left(E_V+1.44\text{eV}\right)$ concentration is increased. By the electron irradiation at more than 160 keV followed by annealing at 950 °C, three deep levels are always observed at 0.30 eV (UK1), 0.58 eV (UK2), and 1.44 eV (HK4). These centers may be defect complexes including carbondisplacement-related defects. All the centers except for the D center are reduced to below the detection limit $\left(1-3\times {10}^{11}{\text{cm}}^{-3}\right)$ by annealing at 1550 °C for 30 min.