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 semi-conductors 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 (Si_1-x-yG_xC_y), monocrystalline Ge_1-xC_x 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 P3m1 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.