Experimental study of Si substitution by Ge in Ge-alloyed SiC epitaxial growth on6H−SiC(0001)

Abstract

The feasability of chemically modified heteroepitaxial growth on $6H\ensuremath{-}\mathrm{SiC}(0001)$ has been investigated to contribute to band-gap engineering in SiC-based technology. A Ge-alloyed SiC:Ge epilayer has been grown on a $3\ifmmode\times\else\texttimes\fi{}3$ reconstructed surface, using repeated growth cycles. Each cycle included a low-temperature molecular-beam epitaxial atomic-layer supply of Si and Ge, followed by carbonization and annealing. The epilayer has been examined in situ by chemical and crystallographic surface analysis tools and ex situ by transmission-electron microscopy. The obtained chemical picture of the Ge uptake consists of a combination of bulk incorporation with buried Ge--C bond formation and a segregated part in the top layers, where Ge atoms are either bound to each other or bound to the Si atoms in excess on the $3\ifmmode\times\else\texttimes\fi{}3$ surface. On the basis of crystallographic local-order analyses, and in agreement with the presence of Ge-C bonds, we demonstrate that the bulklike Ge atoms substitute preferably to Si. The bulk fraction of the grown epilayer appears therefore as an ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}\mathrm{C}$ alloy with x less than 5%.