Synthesis of Butane-Like SiGe Hydrides:Enabling Precursors for CVD of Ge-Rich Semiconductors

摘要

The synthesis of butane-like (GeH_3)_2(SiH_2)_2 (1),(GeH_3)_2SiH(SiH_3)(2),and (GeH_3)_2(SiH_2GeH_2)(3)Si-Ge hydrides with applications in low-temperature synthesis of Ge-rich Si_(1-x)Ge_x 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 (GeH_3)_2(SiH_2)_2 (1)and (GeH_3)_2(SiH_2GeH_2)(3)compounds exist as a mixture of the classic normal (n)and gauche (g)conformational isomers which do not seem to interconvert at 22 deg 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 (GeH_3)_2(SiH_2)_2 (1)species was then utilized to fabricate Si_(0.50)Ge_(0.50)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 deg 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 Ge_2H_6,despite the presence of strong Si-H bonds in the molecular structure.