A novel predictive model for formation enthalpies of Si and Ge hydrides with propane‐ and butane‐like structures

Abstract

Butane- and propane-like silicon-germanium hydrides and chlorinated derivatives represent a new class of precursors for the fabrication of novel metastable materials at low-temperature regimes compatible with selective growth and commensurate with the emerging demand for the reduced thermal budgets of complementary metal oxide semiconductor integration. However, predictive simulation studies of the growth process and reaction mechanisms of these new compounds, needed to accelerate their deployment and fine-tune the unprecedented low-temperature and low-pressure synthesis protocols, require experimental thermodynamic data, which are currently unavailable. Furthermore, traditional quantum chemistry approaches lack the accuracy needed to treat large molecules containing third-row elements such as Ge. Accordingly, here we develop a method to accurately predict the formation enthalpy of these compounds using atom-wise corrections for Si, Ge, Cl, and H. For a test set of 15 well-known hydrides of Si and Ge and their chlorides, such as Si(3)H(8), Ge(2)H(6), SiGeH(6), SiHCl(3), and GeCl(4), our approach reduces the deviations between the experimental and predicted formation enthalpies obtained from complete basis set (CBS-QB3), G2, and B3LPY thermochemistry to levels of 1-3 kcal/mol, or a factor of ∼5 over the corresponding uncorrected values. We show that our approach yields results comparable or better than those obtained using homodesmic reactions while circumventing the need for thermochemical data of the associated reaction species. Optimized atom-wise corrections are then used to generate accurate enthalpies of formation for 39 pure Si-Ge hydrides and a selected group of 20 chlorinated analogs, of which some have recently been synthesized for the first time. Our corrected enthalpies perfectly reproduce the experimental stability trends of heavy butane-like compounds containing Ge. This is in contrast to the direct application of the CBS-QB3 method, which yields erratic predictions. Our approach also provides quantitative bond-additivity rules for the chlorination of these heavier species. Finally, we discuss structure and bonding trends across the entire sequence of butane-, propane-, and ethane-like molecules with a special focus on the isomeric variations.

Ultra-Low-Temperature Epitaxy of Ge-based Semiconductors and Optoelectronic Structures on Si(100): Introducing Higher Order Germanes (Ge3H8, Ge4H10)

“…The bond lengths obtained from our simulations follow the expected trends and are in excellent agreement with those obtained by other authors, and those reported in our prior work on trigermane and tetragermane using slightly smaller basis sets and coarser grids. For example, the shortest Ge–Ge bond lengths (2.444 Å) typically occur between −GeH 3 and −GeH 2 – moieties, while slightly longer values (2.450 Å) prevail between −GeH 3 and −GeH–, or adjoining −GeH 2 – groups.…”

“…According to the thermochemical data in Table the most stable species is i -Ge 4 H 10 , which is consistent with the trends observed in classic butane, where simple gas phase models predict a room temperature equilibrium ratio of ∼9:1 for i -C 4 H 10 / n -C 4 H 10. The calculated vibrational spectra of the tetragermane isomers are shown in Figure (top and bottom corresponding to low- and high-frequency regimes), where they are compared with an experimental spectrum of a gas sample. The latter was obtained from a freshly distilled bulk liquid aliquot which was previously characterized by NMR spectroscopy, showing a mixture of 85% n -Ge 4 H 10 and 15% of i -Ge 4 H 10 , where the 85% can, in principle, be further subdivided into “trans” and “gauche”, which can not be clearly resolved by NMR spectroscopy.…”

Fundamental experimental and theoretical aspects of high-order Ge-hydride chemistry for versatile low-temperature Ge-based materials fabrication

“…The molecular structures and corresponding thermodynamic data for all isomers are summarized in Table 1. The calculated bond lengths exhibit trends very similar to those the we previously reported for tetragermane, 32,34 whose isomers share many of the same geometry and bonding motifs with pentagermane. For example, the shortest Ge-Ge bond lengths (2.444-2.446 Å) are designated as "a" in our table, and connect terminal -GeH 3 and -GeH 2moieties.…”

Molecular Synthesis of High-Performance Near-IR Photodetectors with Independently Tunable Structural and Optical Properties Based on Si–Ge–Sn

“…16 As in the case of the Ge 4 H 10 , the Si 4 H 10 bond lengths calculated from our simulations are in general excellent agreement with those obtained by other authors, and in our prior work and follow expected trends. 19,20 The shortest Si−Si bond lengths (2.351 Å) typically occur between −SiH 3 and −SiH 2 − moieties, while slightly longer values (2.355 Å) are found between −SiH 3 and −SiH−, or adjoining −SiH 2 − groups. In analogy with the Ge analogue, the Si−H bond lengths are also found to follow the expected increasing trend 1.483, 1.486, and 1.490 Å for the −SiH 3 , −SiH 2 −, and −SiH− moieties, respectively.…”