Effects of hydrogen on the formation of SiGe/Si heterostructures
In this report, we review and discuss our results obtained on the surface segregation of Ge atoms and surfactant effects of hydrogen atoms in Si overlayer growth on Ge/Si(100) by gas-source molecular beam epitaxy (GSMBE) using GeH/sub 4/ and Si/sub 2/H/sub 6/. The layer-by-layer growth rate of the Si overlayers was observed in-situ by reflection high-energy electron diffraction (RHEED) intensity oscillation periods.
Surfactant effect of H atoms on the suppression of Ge segregation in Si overgrowth on Ge(n ML)/Si(100) substrates by gas source molecular beam epitaxy
Hydrogen surfactant effect on the surface segregation of Ge atoms has been studied from layer-by-layer changes in the growth rate of Si overlayers on Ge/Si(100) substrates with Ge thicknesses of 0-6 ML by gas source molecular beam epitaxy using Si 2 H 6 . The layer-by-layer growth rates were in-situ measured by reflection high-energy electron diffraction (RHEED) intensity oscillation periods. The growth rate of Si overlayers decreases exponentially with increasing Si thickness and eventually approaches that of Si/Si(100) homoepitaxial growth at substrate temperatures of 440-550°C, which corresponds to the change in surface coverages of Ge atoms. The decay length of the surface concentration of Ge atoms is suppressed by an increase in Si 2 H 6 gas pressure. The temperature dependence of the decay length has an activation energy of 1.3 eV for Si 2 H 6 gas pressures of 5×10 -6 to 5×10 -5 Torr. These facts can be explained as an effect of H atoms existing on the surface
Adsorption and dissociation of Si2H6 on Ge(001)2 × 1
Adsorption and thermally-induced dissociation of disilane (Si2H6) on clean Ge(001)2 × 1 surfaces have been investigated using a combination of Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), reflection high-energy electron diffraction (RHEED), and scanning tunneling microscopy (STM). With initial Si2H6 exposure at room temperature, the Si surface coverage increased monotonically, the EELS surface dangling bond peak intensities continuously decreased, and the intensity of half-order RHEED diffraction rods decreased. The low-coverage Si2H6 sticking probability at 300 K on Ge(001) was found to be ∼ 0.5 while the saturation coverage was ∼ 0.5 ML. A new EELS feature, GSH, involving Si-H and Ge-H bond states was observed at Si2H6 exposures φ ≳ 3.4 × 1013 cm−2. In contrast to Si2H6 -saturated Si(001), the saturated Ge(001) surface significant fraction of dimerized bonds. Adsorbed overlayers were highly disordered with the primary species on saturated surfaces being SiH2, GeH, and undissociated SiH3· Si2H6-saturated Ge(001)2 × 1 substrates were annealed for l min at temperatures Ta between 425 and 825 K. Admolecules were mobile at Ta = 545 K giving rise to significant ordering in one-dimensional chains. By Ta = 605 K, essentially all of the admolecules were captured into coarsened islands. Dangling-bond EELS peaks reappeared by 625 K and the intensities of the half-order RHEED diffraction rods increased. Ge segregation to the surface, which began at Ta ≳ 625 K, occurred rapidly at Ta ⩾ 675 K. All H was desorbed by 725 K.