Midgap levels in both n- and p-type 4H–SiC epilayers investigated by deep level transient spectroscopy

Midgap levels in $n$ - and $p$ -type 4H–SiC epilayers have been investigated by deep level transient spectroscopy (DLTS). The ${\mathrm{EH}}_{6∕7}$ center $(E_{\mathrm{c}}-1.55\mathrm{eV})$ is the dominant midgap level as observed in DLTS spectra for $n$ -type epilayers. The activation energy of ${\mathrm{EH}}_{6∕7}$ center is unchanged regardless of applied electric field, indicating that the charge state of the ${\mathrm{EH}}_{6∕7}$ center may be neutral after electron emission [acceptor-like $(0∕-)$ trap]. In $p$ -type epilayers, a deep level located at $1.49\mathrm{eV}$ above the valence band edge has been detected. The lack of Poole–Frenkel effect in emission time constant from this deep level suggests that this level is donor-like $(+∕0)$ . From the energy level and charge state, this defect center may originate from a single carbon vacancy $\left({\mathrm{V}}_{\mathrm{C}}\right)$ , which has been extensively studied by electron paramagnetic resonance.