Two reaction channels directly observed for atomic hydrogen on the Si(111)-7 x 7 surface

Gas Source Silicon Molecular Beam Epitaxy

Gas source silicon molecular beam epitaxial (Si-MBE) growth is microscopically governed by a disociative adsorption of silicon hydrides, such as Si2H6 source gas molecules on Si surface. The dissociative adsorption generates SiH species on the surface. From this hydride phase, hydrogen desorbs thermaly. The temperature dependence of the growth rate indicated that the hydrogen desorption from the SiH is the rate limiting step. In HBO2 Knudsen cell doping, B adsorbates block the surface migration. Such a blocking effect can be avoided by B2H6 gas dopant, because of the similar incorpration mechanism of B2H6 to that of Si2H6. However, in PH3 gas doping, a crystal quality degradation was observed at a high doping range due to the preferentially high sticking coefficient of PH3 and the resulting surface dangling bond termination. The selective epitaxial growth of a B doped layer using Si2H6 and B2H6 was applied to a novel structured base fabrication for super self-aligned selectively grown base transistor (SSSBT). A successful achievement of the SSSBT fabrication indicates the high potentiality of gas source Si-MBE to the sub-micron size ultra-high speed bipolar large scale integrated (LSI) circuits.

Influences of h on the adsorption of a single ag atom on si(111)-7 × 7 surface

The adsorption of a single Ag atom on both clear Si(111)-7 × 7 and 19 hydrogen terminated Si(111)-7 × 7 (hereafter referred as 19H-Si(111)-7 × 7) surfaces has been investigated using first-principles calculations. The results indicated that the pre-adsorbed H on Si surface altered the surface electronic properties of Si and influenced the adsorption properties of Ag atom on the H terminated Si surface (e.g., adsorption site and bonding properties). Difference charge density data indicated that covalent bond is formed between adsorbed Ag and H atoms on 19H-Si(111)-7 × 7 surface, which increases the adsorption energy of Ag atom on Si surface.

Charge exchange in Li scattering from Si surfaces

Neutral fractions are measured for 4 keV 7Li(+) scattering from clean, hydrogen-covered, and cesiated Si surfaces. The neutral fraction in scattering from clean Si is approximately 26% and it decreases with hydrogen adsorption. When Cs is adsorbed on Si, the neutral fraction does not distinguish the local potential at the Cs sites from the Si sites, unless hydrogen is coadsorbed. These results demonstrate that resonant charge transfer occurs due to coupling of the Li ionization level with the dangling bond surface states, and that the influence of the dangling bonds extends beyond the local scattering sites.