Spin‐coupling and hyperfine interaction of the nitrogen donors in 6H‐SiC

Abstract

The X‐, Q‐band field‐sweep electron spin echo (FS ESE) study of n‐type 6H‐SiC wafers shows besides the well known hyperfine (hf) triplet lines of 14N on two quasi‐cubic (Nc1, Nc2) and hexagonal (Nh) sites additional triplet lines (Nx) of comparatively low intensity with a g ‐tensor of about the average value of the Nc2 and Nh spectrum at 4.2 K. The Nx triplet has half of the hf splitting with respect to the nitrogen residing at cubic sites Nc2. Pulsed electron nuclear double resonance (ENDOR) measurements performed on the Nx EPR triplet line demonstrate that there is an efficient spin‐coupling between Nh and Nx nitrogen related centers. The Nx triplet lines were attributed to distant donor Nc–Nh pairs between nitrogen atoms residing at quasi‐cubic and hexagonal sites having a total electron spin S = 1, which were found before in n‐type 4H‐SiC. Based on Q‐band FS ESE and X‐band pulsed ENDOR measurements the values of the hf interaction for Nc1, Nc2 were reassigned with respect to the assignment accepted hitherto.The super hyperfine (shf) interaction with neighboring atoms of nitrogen on the quasi‐cubic lattice sites was studied by FS ESE and pulsed ENDOR. The new shf lines due to 29Si and 13C atoms with large shf interaction which were not observed previously were found in nitrogen FS ESE and ENDOR spectra. One of them, with the largest shf splitting (23.12 MHz), were attributed to the 29Si atoms along the c‐axis in nearest‐neighbor positions of nitrogen on the quasi‐cubic sites which unambiguously confirms that nitrogen substitute carbon lattice site in 6H‐SiC. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic structure of the nitrogen donors in 6H SiC as studied by pulsed ENDOR and TRIPLE ENDOR spectroscopy

“…But despite of the conclusion made on the basis of this ENDOR study of N donors some fundamental questions related to the spatial distribution of the electronic wave function of the isolated N donors residing at the two quasi‐cubic sites in 6H‐SiC were not well understood yet. A major obstacle in previous ENDOR studies of the N donors at cubic sites 15 was that the 29 Si and 13 C ENDOR signals could not be unambiguously assigned to either the N k1 or N k2 site. Furthermore the shf lines observed in the EPR and ENDOR spectra could not be ascribed to specific C and Si atoms located around the N k1 and N k2 sites in 6H SiC as well as the relative sign of the shfi constants for N donors were not obtained yet.…”

“…With the aim to find the shf lines with the larger constants just as obtained for 4H SiC, N donors were studied by EPR 13, field sweep electron spin echo, (FS ESE) and pulsed ENDOR methods in 6H SiC 15. Shf satellite lines were also found in 14 N EPR and FS ESE spectra, which correspond to shfi constants significantly larger than those observed previously in the ENDOR spectra of 6H SiC and confirmed in that way that a careful pulsed ENDOR study in the high‐frequency range is also required for this polytype.…”

Theoretical and electron paramagnetic resonance studies of hyperfine interaction in nitrogen doped 4H and 6H SiC

“…14 As shown in Fig. 3, these C hf structures are best fitted with assuming the hf interactions with 6 and 3 equivalent 13 C atoms, respectively, as predicted from the calculations ($20.4 MHz for six C-atoms and $14.6 MHz for three C atoms). The agreement between EPR and calculations in the Si hf structure of N C (k 1 ) and the C hf structures of N C (k 2 ) supports the conclusion that the missing of the Si hf structure of N C (k 2 ) can be explained by the nature of the floating states, i.e., the spin density is distributed in the interstitial channels around the Si atoms, and it does not require the model of N substituting Si atom at k 2 site in 6 H SiC.…”

“…10: In both 4 H an 6 H SiC, this interaction is weak for N C (h), and strong when N resides at the quasi-cubic sites. However, the previous results about the hf structure of N donor for proximate 13 C and 29 Si isotopes in 4 H and 6 H SiC (Refs. 10-14) are contradictory.…”

“…In 6 H SiC, Duijn-Arnold et al 12 observe that the spin density is localized mainly on C atoms not only for the quasi-cubic sites but also for the N C (h), and no strong hf interaction is found with Si atoms. For the quasi-cubic N donors, Savchenko et al 13 find the strongest hf interaction with Si atoms close to the N donor, however considerable hf interaction is obtained for C atoms too. In their later study, 14 large hf splitting is found for several Si atoms for N C (h) and N C (k 1 ).…”