Electrical properties of highly nitrogen-doped 6H-SiC single crystals: Microwave cavity perturbation study

The silicon carbide (SiC) single crystals of 6H polytype with nitrogen donor concentration ND – NA) ≈ 1∙1017 ...4∙1019 cm –3 grown using the modified Lely method were studied applying the cavity perturbation method. From the temperature dependence of the resonant frequency shift and microwave loss of the cavity loaded with samples under study, the temperature dependence of the conductivity was estimated. From the temperature dependence of the natural logarithm of conductivity versus 1000/T, the activation energies for processes corresponding to electron transitions from impurity levels to the conduction band (ε1) and electron hopping over nitrogen donors in the D0 bands (ε3) were determined. It was found that in 6H-SiC ε1 = 50 meV for (ND – NA) ≈ 1∙10 17 cm –3 , ε1 = 32 meV and ε3 = 6 meV for (ND – NA) ≈ 1∙1019cm–3 , ε1 = 13.5 meV and ε3 = 3.5 meV for ((ND – NA) ≈ 4∙1019 cm–3.