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

摘要

Midgap levels in n- and p-type 4H-SiC epilayers have been investigated by deep level transient spectroscopy (DLTS). The EH_(6/7) center (E_c-1.55 eV) is the dominant midgap level as observed in DLTS spectra for n-type epilayers. The activation energy of EH_(6/7) center is unchanged regardless of applied electric field, indicating that the charge state of the 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 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 (V_C), which has been extensively studied by electron paramagnetic resonance.