Room-temperature growth of submonolayers of silicon on Si(001) studied with scanning tunneling microscopy

Abstract

Room-temperature deposited submonolayers of silicon on Si͑001͒ are investigated using STM. The observed structures and the mechanisms leading to their formation are discussed. Isolated ad-dimers in different geometries are described and a kinetic model for their formation is deduced. It is shown how further growth occurs via the formation of 3-atom clusters, which act as nucleation centers for the formation of two types of linear structures. One of the line types is formed in the ͓110͔ direction, and has been observed before. The other is in the ͓310͔ direction. At a coverage of nearly 0.2 ML a kind of random network consisting of segments of the two types of atomic lines is formed. Above 0.2 ML coverage these lines are converted into epitaxial dimer rows. A pathway for this conversion is proposed on the basis of experimental observations.

Early stage of Ge growth on Si(001) vicinal surfaces with an 8° miscut along[110]

“…2͑b͔͒. Their variable length suggests that they originate from an aggregation process of single addimers, as is supported by previous works 25,28,29 on different configurations of Ge and Si addimers on the Si͑001͒ surface. Nevertheless, in our case, chains have a preferential attachment site, as schematically illustrated in Fig.…”

“…Taking the edge of the D B step as a reference point, the zigzag chain is located two lattice parameters away from the step edge. The zigzag chain consists of dimers located in two alternate positions between dimers 1 and 2 of the terrace: One dimer is situated within a row of the p͑2 ϫ 2͒ reconstruction and corresponds to the most stable configuration 28,29 while the other one lies between two adjacent rows. Taken together, they form a chain which reduces the tensile strain energy of dimer bonds located along the base of the D B step edges, particularly for small terrace widths.…”

“…7 It must be noted that the position of the shifted step edge coincides with that of the zigzag chain which behaves as an epitaxial segment. 29 So zigzag chains allow the enlargement of the upper terrace and promote the shift of the D B step edge, starting the step flow process. By increasing the coverage, the flow of regular trains of D B steps produces the disconnected domains seen in Fig.…”

Atomic details of step flow growth on Si(001)

“…Single adatoms can also be attached to the configurations 4 and 5. In case of configuration 4 this yields the formation of a three-atom cluster, 14 right at the step edge, as has been observed a few times. Attachment of an adatom at configuration 5 yields the configuration 6 shown in Figs.…”

“…The majority of the dimer rows ends with a dimer in the trough of the lower terrace ͓see configuration 0 in Figs. 1͑a͒ and 1͑b͒; note the pronounced appearance of the lower terrace dangling bonds in the empty- 14,18 Positioning the adatom at the center of the dimer row ͑configuration 1a͒ gas a thirty times higher population than the site of configuration 1b. The dimer row of the upper terrace can be extended with a dimer by adding another adatom.…”