Radiotracer identification of a Ta-related deep level in 4H–SiC

To identify tantalum-related deep levels, deep level transient spectroscopy (DLTS) measurements were performed on Ta-implanted n-type 4H–silicon carbide. The DLTS spectra of samples implanted with stable Ta181 exhibit one dominating peak representing a trap energy of about ET=EC−0.67 eV. Due to superimposed signals of intrinsic defects, the exact value depends on the annealing conditions. To achieve a definite assignment of this peak to tantalum, the radioactive isotope Ta177 was recoil implanted into n-type 4H–SiC. DLTS spectra measured subsequently during the nuclear decay of Ta177 to Hf177 reveal a trap with decreasing concentration according to the elemental transmutation. This effect definitely proofs the identification of a Ta-related level at 0.68 eV below the conduction band edge. There is no further DLTS peak of time-dependent height, indicating that there is no deep level of Hf in the part of the band gap investigated.