EPITAXIAL-GROWTH OF SIC THIN-FILMS ON SI-STABILIZED ALPHA-SIC(0001) AT LOW-TEMPERATURES BY SOLID-SOURCE MOLECULAR-BEAM EPITAXY

Epitaxial growth of SiC on alpha-SiC(0001) substrates was carried out at relatively low temperatures (900-1000 degrees C) and high growth rates (about 1 nm/min), by means of solid-source molecular beam epitaxy controlled by a quadrupole mass spectrometry based flux meter. The films were obtained on silicon-stabilized surfaces showing (3 x 3) and (2 x 2) superstructures. The reflection high-energy electron diffraction (RHEED) and transmission electron microscopy (TEM) investigations show, independent of the surface orientation, that the film growth can be quantified in two steps: In the initial stage of growth, at first the Si-determined superstructure will be formed. Despite the low temperature, growth of SiC then proceeds in a layer-by-layer mode leading to flat film-substrate interfaces. This result demonstrates the significance of surface reconstruction for the growth process, corresponding to results recently obtained using gas source molecular beam epitaxy. The films grow by stacking of laminae of alpha-and beta-SiC, respectively, which may be attributed to fluctuations in the Si adlayer thickness. Films grown on off-oriented substrates contain many defects, likely double-positioning boundaries, directly associated with surface steps. For increasing film thickness during the film growth this boundaries may be eliminated. Films grown on well-oriented substrates show only a few of these defects. In case of increasing Si excess flux during the growth, the TEM investigations, RHEED patterns and damped RHEED-oscillations indicate an abrupt change in the growth process. This is due to the formation of Si islands on the film surface and the SiC island growth by carbonization of these islands. Only beta-SiC was found in this case.