Space charge formation in the high purity semi-insulating bulk 4H–silicon carbide

•Positive space charge formation in the HPSI bulk 4H-SiC due to blocking contacts.•Presence of the dispersed wide impurity band below the Fermi level.•Very short carrier lifetime τe ≤ 1 ns, saturation electron drift velocity vs = 8.7 × 106 cm2s-1.•Theoretical model considering electron mobility damping consistently fit all results.•Evaluation procedure is applicable for various SI semiconductors with short carrier lifetime.