A comprehensive study of the etching behaviour of threading dislocations in n-type substrates and n- and p-type homo-epitaxial layers was performed. Defect selective etching in molten KOH was applied to a large number of substrates and homo-epitaxial layers covering the maximum available doping range in order to identify etching regimes and the influence of doping upon the etch pattern. The types of threading dislocations present in n-type 4H–SiC substrates and n- and p-type homo-epitaxial layers were investigated by synchrotron X-ray topography. Based upon the visibility criterion g•b = 0, two types of threading dislocations, named TED II and TED III, were identified and reported for the first time. For a representative sample of each etching regime, the dislocation pattern obtained by synchrotron X-ray topography was compared to the etch pattern in order to verify the etching method especially with respect to the interpretation of etch pits based upon their shape and size. A 1:1 correlation between etch pits and dislocations was found for all of the samples and for all doping levels. The etch pit density on the Si-face coincided with the dislocation density at the sample surface. The sample’s doping state had to be taken into account for the determination of the respective densities of different dislocation types such as threading edge or threading screw dislocations and micropipes. In the case of highly-doped n-type substrates, the results showed that it was not possible to distinguish all dislocation types by the size and shape of their etch pits, regardless of etching parameters. In the case of p-type and low n-type samples, threading screw dislocations could be distinguished from all types of threading edge dislocations by the size of their etch pits. An additional etch pit type was observed in n-type samples with a doping level in the range of 2 x 1016 to 1018/cm3. This additional etch pit type was correlated with threading edge II dislocations.

Threading Dislocations in n- and p-Type 4H–SiC Material Analyzed by Etching and Synchrotron X-Ray Topography. B.Kallinger, S.Polster, P.Berwian, J.Friedrich, G.Müller, A.N.Danilewsky, A.Wehrhahn, A.D.Weber: Journal of Crystal Growth, 2011, 314[1], 21-9