Spin exchange dynamics in 4H SiC monocrystals with different nitrogen donor concentrations

4H silicon carbide (SiC) polytype is preferred over other SiC polytypes for high-power, high-voltage, and high-frequency applications due toits superior electrical, thermal, and structural characteristics. In this manuscript, we provide a comprehensive study of the spin couplingdynamics between conduction electrons and nitrogen (N) donors in monocrystalline 4H SiC with various concentrations of uncompensatedN donors from 10(17)to 5 x 10(19)cm(-3)by continuous wave, pulsed electron paramagnetic resonance (EPR), and microwave perturbation techniques atT= 4.2-300 K. At low temperatures, two triplets due to N donors in cubic (N-k) hexagonal (N-h) positions and triplet arisen from spin-interaction between N-h and N-k were observed in 4H SiC having N-d-N-a approximate to 10(17)cm(-3). A single S-line (S= 1/2) dominates the EPRspectra in all investigated 4H SiC monocrystals at high temperatures. It was established that this line occurs due to the exchange coupling of localized electrons (dominate at low temperatures) and non-localized electrons (dominate at high temperatures). The localized electronswere attributed to N-h for N-d-N-a approximate to 10(17)cm(-3)andN(k )donors for N-d-N-a >= 5x10(18)cm(-3). We have concluded that the conduction electronsin 4H SiC monocrystals are characterized by g(||)= 2.0053(3) and g(perpendicular to)= 2.0011(3) for N-d-N-a <= 5x10(18)cm(-3)andg||= 2.0057(3) andg(perpendicular to)= 2.0019(3) forN(d)-N-a approximate to 5x10(19)cm(-3). Using the theoretical fitting of the temperature variation of S-line EPR linewidth in 4H SiChaving N-d-N-a <= 5x10(18)cm(-3), the energy levels of 57-65 meV that correlate with the valley-orbit splitting values for N-k donors in 4H SiCmonocrystals were obtained.