Deep levels in low-energy electron-irradiated 4H-SiC

Deep levels introduced by low-energy (200 keV) electron irradiation in n-type 4H-SiC epitaxial layers grown by chemical vapour deposition were studied by deep level transient spectroscopy (DLTS) and photoexcitation electron paramagnetic resonance (photo-EPR). After irradiation, several DLTS levels, EH1, EH3, Z1/2, EH5 and EH6/7, often reported in irradiated 4H-SiC, were observed. In irradiated freestanding films from the same wafer, the EPR signals of the carbon vacancy in the positive and negative charge states, VC+ and VC-, respectively, can be observed simultaneously under illumination with light of certain photon energies. Comparing the ionization energies obtained from DLTS and photo-EPR, we suggest that the EH6/7 (at ∝EC-1.6 eV) and EH5 (at ∝EC-1.0 eV) electron traps may be related to the single donor (+ vertical stroke 0) and the double acceptor (1- vertical stroke 2-) level of VC, respectively. Judging from the relative intensity of the DLTS signals, the EH6/7 level may also be contributed to by other unidentified defects. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)