Synthesis of butane-like SiGe hydrides: Enabling precursors for CVD of Ge-rich semiconductors

The synthesis of butane-like (GeH3)(2)(SiH2)(2) (1), (GeH3)(2)SiH(SiH3) (2), and (GeH3)(2)(SiH2GeH2) (3) Si-Ge hydrides with applications in low-temperature synthesis of Ge-rich Si1-xGex optoelectronic alloys has been demonstrated. The compositional, vibrational, structural, and thermochemical properties of these compounds were studied by FTIR, multinuclear NMR, mass spectrometry, Rutherford backscattering, and density functional theory (DFT) simulations. The analyses indicate that the linear (GeH3)(2)(SiH2)(2) (1) and (GeH3)(2)(SiH2GeH2) (3) compounds exist as a mixture of the classic normal (n) and gauche (g) conformational isomers which do not seem to interconvert at 22 degrees C. The conformational proportions in the samples were determined using a new fitting procedure, which combines calculated molecular spectra to reproduce those observed by varying the global intensity, frequency scale, and admixture coefficients of the individual conformers. The (GeH3)(2)(SiH2)(2) (1) species was then utilized to fabricate Si0.50Ge0.50 semiconductor alloys reflecting exactly the Si/Ge content of the precursor. Device quality layers were grown via gas source MBE directly on Si(100) at unprecedented low temperatures 350-450 degrees C and display homogeneous compositional and strain profiles, low threading dislocation densities, and atomically planar surfaces. Low energy electron microscopy (LEEM) analysis has demonstrated that the precursor is highly reactive on Si(100) surfaces, with H-2 desorption kinetics comparable to those of Ge2H6, despite the presence of strong Si-H bonds in the molecular structure.