Step bunching behaviour on the {0001} surface of hexagonal SiC

Surface topography of the {0 0 0 1} facet plane of as-grown 6H- and 4H-SiC crystals was studied ex situ by Nomarski optical microscopy (NOM) and atomi c force microscopy (AFM). The surface polarity and the polytype of grown cr ystals largely affect the growth surface morphology of SiC{0 0 0 1} via dif ferences in several thermodynamic and kinetic parameters. NOM observations revealed giant steps of a few micrometers in height on the {0 0 0 1} growth facet, and it was found that a morphological transition of the growth face t occurred when the growth conditions were changed, AFM imaging of the step ped structure of SiC{0 0 0 1} detected steps of height equal to the unit c- lattice parameter {c = 1.512 nm for 6H-SiC and 1.005 nm for 4H-SiC}. They a re fairly straight and very regularly arranged, giving rise to equidistant step trains. Upon nitrogen doping, these regular step trains on the 6H-SiC( 0 0 0 (1) over bar)C and 4H-SiC(0 0 0 (1) over bar)C surfaces became unstab le: the equidistant step trains were transformed into meandering macrosteps of height greater than 10 nm. In this paper, we discuss the mechanism of m acrostep formation (step bunching) on the SiC{0 0 0 1} surfaces through the consideration of the interplay between step energetics (repulsive step int eraction) and kinetics (asymmetric step kinetics) on the growing crystal su rface and elucidate how they affect the growth surface morphology of the Si C{0 0 0 1} facet. (C) 2000 Elsevier Science B.V. All rights reserved.