The structural characteristics of commercial 4H and 6H p-type Al-doped substrate crystals were studied. A radial non-uniformity of the extended defect distribution over the substrates was found to be a typical feature of substrates which were grown by using the modified Lely method. In the central region of the wafers, a relatively uniform distribution of dislocations with a density of less than 105/cm2 was observed. In the peripheral regions of the crystals, the dislocation density exceeded 106/cm2 and was highly non-uniform.

Structural, Electrical and Optical Properties of Bulk 4H and 6H p-Type SiC. E.V.Kalinina, A.S.Zubrilov, N.I.Kuznetsov, I.P.Nikitina, A.S.Tregubova, M.P.Shcheglov, V.Y.Bratus: Materials Science Forum, 2000, 338-342, 497-500