AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM1
H Transfer and Ge/Si Site Exchange during Germane Adsorption at Si(001)

Wednesday, November 5, 2003, 8:20 am, Room 328

Session: Adsorption on Semiconductor Surfaces
Presenter: T. Murata, Tohoku University, Japan
Authors: T. Murata, Tohoku University, Japan
M. Suemitsu, Tohoku University, Japan
Correspondent: Click to Email
Germane adsorption at Si(001) is important as an initial elementary step for Ge/Si heteroepitaxy. It also provides an ideal platform to investigate Ge adsorption at Si sites, one of the elementary processes in SiGe epitaxy. Little is known, however, on its details. Among the remaining issues are whether H atoms from germane are transferred to Si atoms or they stay intact at Ge sites and whether a site exchange occurs between Si and Ge during adsorption. To tackle these problems, we have combined TPD and multiple-internal-reflection FTIR, and have investigated the Si(001) surface adsorbed with germane at room temperature. These two methods form a complementary pair since TPD backs up the quantitative aspect of the characterization while FTIR is most powerful in state-resolved analysis. The findings we present here are (1) that almost all the H atoms are transferred from germane to Si atoms and (2) that the site exchange does occur between Si and Ge even at room temperature. The finding (1) is supported by exhaustive dominance of both the SiH-related @beta@@sub 1@ desorption peak in TPD and the SiH-related stretching band in FTIR. Persistence of these SiH-related signatures up to ~1ML of hydrogen coverage is hardly understood without considering a site exchange between substrate Si and adsorbed Ge atoms, leading us to the conclusion (2). Recent ab-initio calculations suggest that the two findings originate from a single event: adatom diffusion. According to Jeong and Oshiyama,@footnote 1,2@ Si adatom diffusion on Si(001):H surface proceeds via release of the H atom from the adatom to a substrate Si atom, site exchange between the adatom and another substrate Si atom, and capture of the H atom by a "new" adatom. The larger Si-H bonding energy in excess of 30 meV/atom than that of Ge-H may stabilize the Si-H/Ge state once formed. @FootnoteText@ @footnote 1@ Jeong and Oshiyama: Phys. Rev. B58(1998)12958.@footnote 2@ Jeong and Oshiyama: Surface Science 436(1999)L666.