Investigation of single crystals and epitaxial layers (EL) Of SiC by means of real color SEM technique

Abstract

Investigations were undertaken with SiC, a large-bandgap semiconductor material, that is rather promising for designing different optoelectronic devices. The characteristic feature of SiC is the availability of a large number of modifications, i.e. polytypes, strongly differing in the band-gap. The important problems that stand in the way of mastering SiC are the detectable doping of single crystals and epitaxial structures, the transformation of polytypes, and the structure of the intermediate layer. Crystals of SiC and its EL of 3C, 15R, 6H, 4H polytypes doped with N, Al, Ga and B were investigated. Single crystals were grown by the Leli method at T = 2600-2700°C as plates with basis planes {0001} . Epitaxial layers were grown by the sublimation "sandwich method" at T = 1700-2400°C in a vacuum or in an argon atmosphere.An analysis of the luminescence micrographs in the SEM and of the CL spectra shows that the distribution of impurities and polytype inclusions in single crystals considerably differs from that in EL. In the first case there occurs a striated inhomogeneity of CL across the whole width of the crystal which is obviously connected with an inhomogeneous distribution of dopes. Such a distribution of impurities was not observed in EL.