EPR spectra of the excited nitrogen state in 6H-SiC

A study is reported of donor EPR spectra in compensated 6H-SiC crystals with donor concentrations (N _D -N _A ) varied from 8×10¹⁷ to 5×10¹⁶ cm^?3, performed within a temperature interval from 77 to 170 K at a frequency of 37 GHz. A second paramagnetic state of nitrogen in silicon carbide has been found to exist, and it is associated with its excited 1S(E) state becoming paramagnetic after thermal ionization of the donor electrons from the 1S(A ₁) to 1S(E) level. The EPR spectrum of nitrogen in the 1S(E) state is a single line with an anisotropic width because of the unresolved hyperfine structure. A light-induced charge transfer between the ground, 1S(A ₁), and excited, 1S(E), nitrogen states has been observed. The valley-orbit splitting and the energy required to ionize donor electrons from the 1S(E) to higher lying excited states have been determined for the cubic nitrogen sites. The parameters of a structural defect, characteristic of n-type 6H-SiC compensated crystals, have been established.