Gas-surface reactivity in mixed-crystal systems:: the reaction of GeH4 and Ge2H6 on Si surfaces

[摘要] Supersonic molecular beam techniques have been employed to examine the dissociative adsorption of GeH4 and Ge2H6 on the Si(100) and Si(111) surfaces. At sufficiently high incident kinetic energies (greater than or equal to 1 eV), both species on both surfaces react via a direct dissociation mechanism. At sufficiently low incident kinetic energies (less than or equal to 0.6 eV) and substrate temperatures, however, dissociation of Ge2H6 on the Si(100) surface proceeds primarily through a trapping, precursor-mediated dissociation channel. Study of this mixed-crystal system, i.e., GenH2n+2 on Si, has permitted important comparisons to two related systems: the reactions of these same gas phase species (GeH4 and Ge2H6) on Ge surfaces, and the reactions of silanes (SiH4 and Si2H6) on these same Si surfaces. We find that the Si surfaces are much more reactive (as much as a factor of 10) than their Ge counterparts, whereas, under similar reaction conditions, and on the same Si surface, the Ge hydrides are moderately more reactive (approximate to factor of 2) than the Si hydrides. The reactivity of ultrathin (approximate to 2 monolayers) Ge(a) epitaxial layers has also been examined. On Si(100), these strained Ge epitaxial layers exhibit a reactivity that is intermediate between those observed on clean Si(100) and on clean (bulk) Ge(100) surfaces. This example illustrates the role that strain can play in gas-surface reactivity, heretofore, an almost unexamined subject. On the other hand, on Si(111), the Ge epitaxial layer is less reactive than both clean elemental surfaces, and this behavior is attributed to intrinsically low reactivity exhibited by the Ge-induced (5 x 5) reconstruction known to form on this surface. (C) 1997 Elsevier Science B.V.

[发布日期] 1997-12-10

[关键词] adsorption kinetics;epitaxy;germanium;molecule-solid reactions;semiconductor-semiconductor heterostructures;silicon;sticking;surface chemical reaction