Theory of metastable group-IV alloys formed from CVD precursors

Abstract

Using chemical-vapor deposition ͑CVD͒ precursors, group-IV compounds such as Si 4 C and Ge 4 C, which incorporate 20 at. % carbon, have been synthesized. Here we present systematic ab initio studies of the electronic and structural properties of group-IV compounds formed from CVD precursors. We also propose a class of precursor molecules for materials containing 25 at. % carbon. These compounds are energetically comparable to already synthesized materials ͑e.g., Ge 4 C) and are semimetallic within the local-density approximation. In addition, we give information for two previously proposed group-IV compounds, Si 2 Sn 2 C and Ge 3 SnC, which are direct-gap semiconductors and match the lattice of silicon to within 1%.We use the ab initio pseudopotential method 31 in the local-density approximation ͑LDA͒ with norm-conserving pseudopotentials 32 in a nonlocal form suggested by Kleinman and Bylander.

Novel Si–Ge–C superlattices and their applications

“…However, it was demonstrated by MBE growth that Si 4 C (20% C) ordered alloys can be pseudomorphic on Si [13,14]. Theoretical studies [15] have analyzed the precursor molecules for CVD growth, the corresponding crystal structures, and the band structures for Si 4 C, as well as other ordered alloys with high C content. The band structures were not calculated for films strained to Si, but rather for ''bulk'' materials, relaxed to their natural lattice constants, which would require substrates with suitable lattice constants, a problem without an obvious solution.…”

“…The lattice mismatch, relative to Si, of Si 4 C is À8.1%, [15] while for Ge, it is +4.2%. These values make it impossible to grow thick pseudomorphic layers of Si 4 C, but it is feasible to grow the few atomic planes necessary to construct short period SLs strained to Si.…”

Novel Si-Ge-C superlattices and their applications

“…However, it was demonstrated by MBE growth that Si4C (20% C) ordered alloys can be pseudomorphic on Si [5,6]. Theoretical studies [7] have analyzed the precursor molecules for CVD growth, the corresponding crystal structures, and the band structures for Si4C, Ge4C, Sn4C, and other ordered alloys with high C content. The band structures were not calculated for films strained to Si, but rather for "bulk" materials, which would require substrates with suitable lattice constants, a problem without an obvious solution.…”

“…The band structures were not calculated for films strained to Si, but rather for "bulk" materials, which would require substrates with suitable lattice constants, a problem without an obvious solution. The lattice mismatch, relative to Si, of Si4C and Ge4C, is -8.1% and -3.7%, respectively (+4.2% for Ge) [7]. Those values make it impossible to grow pseudomorphic thick layers of Si4C and Ge4C, but it is feasible to grow the few atomic planes necessary to construct short period SLs.…”

Electronic and optical properties of zinc-blende GeC by first principles study

“…6 For example, Kouvetakis and co-workers 7 reported that a Ge 4 C compound with diamond-like tetrahedral bonding was yielded by thermal decomposition of C(GeH 3 ) 4 compound at 500 • C using ultrahigh-vacuum CVD. Subsequently, Zhang et al 8 theoretically proposed Ge 4 C and Ge 3 C compounds on the basis of the crystal structure of methylgermanes precursor molecules. The electronic band structures calculated by the local density approximation (LDA) method revealed that Ge 4 C compound has a small indirect band gap of 0.4 eV, while Ge 3 C compound shows metallic features.…”