EPR, ESE and pulsed ENDOR study of the nitrogen donor pairs on quasi-cubic lattice sites in 6H SiC

D-band EPR, X-band FS ESE and pulsed ENDOR studies of the additional nitrogen (N) related centers observed in highly compensated n-type 6H-SiC wafers are presented. The D-band EPR and X-band FS ESE spectrum consists of the 14N hyperfine (hf) triplet lines of the N donors incorporated at the two quasi-cubic (Nc1, Nc2) sites with the intensity ratio of INc1/INc2=0.7 and three additional triplet lines. X-band pulsed ENDOR spectra have shown intense 14N ENDOR signals of Nc1, Nc2 centers and new 14N lines due to the N related centers N1, N2, N3 with the isotropic hf splitting: 21.04, 26.43, 29.77 MHz, respectively. It was found that the g-tensors of the N2 and N3 triplet lines coincide with those of N on quasi-cubic Nc2 site. The g-tensor of the third N1 triplet lines corresponds to the average value of the Nc1 and Nc2 spectrum: g(N1)≈12[g(Nc1)+g(Nc2)]. It was suggested that N1 center with Aiso=21.04 MHz is due to the spin coupling between N on two quasi-cubic Nc1 and Nc2 sites while two others are tentatively attributed to the N pairs formed between N atoms on one quasi-cubic Nc2 site.