Shape change of SiGe islands with initial Si capping

Abstract

The morphologies of self-assembled Ge∕Si(001) islands with initial Si capping at a temperature of 640°C are investigated by atomic force microscopy. Before Si capping, the islands show a metastable dome shape with very good size uniformity. This dome shape changes to a pyramid shape with {103} facets at a Si capping thickness of 0.32nm, and then changes to pyramid shapes with {104} and {105} facets at Si capping thicknesses of 0.42 and 0.64nm, respectively. Noteworthy is that islands with one side retained their dome shape while the other three sides that changed to {103} facets are observed at a Si capping thickness of 0.18nm. These observations indicate that island shape change with Si capping is a kinetic rather than thermodynamic process. The atomic processes associated with this island shape change are kinetically limited at a low temperature of 400°C, and no significant change in size and shape of islands is observed when Si capping layers are deposited at this temperature.

Atomic composition profile change of SiGe islands during Si capping

“…1͑c͒ and 1͑d͒. As suggested by Wu et al 12 these observations indicate that the shape change of SiGe islands during Si capping at 640°C is a kinetic rather than a thermodynamic process.…”

“…As shown in Fig. 1͑a͒, before Si capping the SiGe islands are dome-shaped, and this dome shape transforms to a ͕103͖-faceted pyramid 12 at a Si capping thickness of 0.32 nm, as shown in Fig. 1͑b͒.…”

Formation of planar defects over GeSi islands in Si capping layer grown at low temperature

“…The substrate temperature was then lowered to 640°C, and a 50-nm-thick Si buffer layer was grown at a growth rate of 0.08 nm/s. For the island growth, a two-step growth method was employed to improve the uniformity of islands 4,5 in which a 0.8-nm-thick Ge layer was first deposited, followed by a 5 min growth interruption before another 0.05-nm-thick Ge layer was deposited. The growth temperature and rate were 640°C and 0.01 nm/s, respectively.…”

“…For a GeSi islands multilayer, Si spacer layers are grown to separate the islands in different layers. 3 Previous investigations revealed that, after Si capping at a high temperature, the GeSi island shape changes from a dome to a pyramid 4 and to a ring, 5 whereas, by means of low temperature deposition, GeSi islands are embedded into a Si matrix without altering appreciably their shape and composition. 6 If one wants to use the islands as stressors to introduce a strain, thus to increase the electron mobility in the Si capping layer, the preservation of island morphology is useful.…”

Reversible Reshaping of Supported Metal Nanoislands Under Reaction Conditions in a Minimalistic Lattice Model

“…Note that the term "reshaping" may generally have slightly different meanings. Examples are the reorientation of islands on substrates as a result of various factors [7,19,39], fluctuations of the shape around an assumed equilibrium circular shape [20], tuning of the length-to-width ratio by changing the substrate characteristics [23], dome to pyramid shape change of 3D islands [47] or a sequence of close island shapes resulted from the increase of the strain [6]. The present paper deals with the unfolding of initially compact islands into strongly ramified (fractal-like) structures.…”