Synthesis and atomic and electronic structure of new Si-Ge-C alloys and compounds

The synthesis and characterization of completely novel binary and ternary alloy semiconductors and ordered phases based on C, Si, and Ge are discussed in this review. Metastable compound semiconductors with ordered structures, which include stoichiometric SiGe, Si4C, Si3GeC4 (sphalerite), Ge4C, (Si2Ge)C-x, and (Ge2Si)C-x (x = 5%), are described. Materials systems include diamond-structured silicon-germanium solid solutions with dissolved carbon (Si1-x-yGexCy), monocrystalline Ge1-xCx hybrids of Ge, and C-diamond and related Si-containing random alloy systems. The Si4C and Ge4C materials incorporate the corresponding tetrahedra that are linked together to form a diamond-cubic structure related to Si. The Si3GeC4 phase is related to sphalerite and (Si2Ge)C-x has a new P (3) over bar m1 structure formed by Ge-Si-Si ordering along the diamond [111] direction. These compounds offer the prospect of band gaps wider than that of Si; in some cases, the band gaps are expected to become direct. This report emphasizes an approach that combines novel precursor chemistries and modern deposition techniques (ultrahigh-vacuum chemical-vapor deposition) to develop heteroepitaxial, device-quality inorganic materials. Important highlights of recent research based on conventional deposition methods are also summarized.