Atomic composition profile change of SiGe islands during Si capping

Abstract

The 6% Ge isocomposition profile change of individual SiGe islands during Si capping at 640°C is investigated by atomic force microscopy combined with a selective etching procedure. The island shape transforms from a dome to a {103}-faceted pyramid at a Si capping thickness of 0.32nm, followed by the decreasing of pyramid facet inclination with increasing Si capping layer thickness. The 6% Ge isocomposition profiles show that the island with more highly Si enriched at its one base corner before Si capping becomes to be more highly Si intermixed along pyramid base diagonals during Si capping. This Si enrichment evolution inside an island during Si capping can be attributed to the exchange of capped Si atoms that aggregated to the island by surface diffusion with Ge atoms from inside the island by both atomic surface segregation and interdiffusion rather than to the atomic interdiffusion at the interface between the island and the Si substrate. In addition, the observed Si enrichment along the island base diagonals is attempted to be explained on the basis of the elastic constant anisotropy of the Si and Ge materials in (001) plane.

Designer Ge/Si composite quantum dots with enhanced thermoelectric properties

“…Based on the selectivity of a H 2 O 2 -or BPAcontaining solution, that etches preferentially Ge over Si, it was possible to follow the time evolution of the etching process and to determine the spatial distribution of Si and Ge in Ge QDs with a resolution of a few nanometers. 18,[24][25][26] In this study, selective chemical etching was conducted on the CQD samples at rt to reveal their composition distributions as well as to study their formation mechanisms. A mixture of NH 4 OH, H 2 O 2 , and deionized water was used as the etchant that selectively removes Ge over Si at rt and has an extremely low etching rate for the SiGe alloy with Ge composition less than 30%.…”

“…Hence, the etching experiment discloses orderly square plateaus under the 2-fold CQDs that have a 1 nm-thick Si inserting layer. For those CQDs with a thicker inserting layer of Si, the excess Si deposited over the already alloyed pyramids may be expelled from the pyramid apex to its sides or corners based on thermodynamic or kinetic considerations, 25,29,30 thus resulting in a fortress-like isocompositional prole [Fig. 2(e)].…”

Compositional mapping of semiconductor quantum dots and rings

“…The same technique has been applied to the study of Ge/Si islands overgrown with Si [123,151,152]. If the proper growth protocol is employed, this leads to the formation of quantum rings.…”

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

“…This shape change is related to the anisotropy of the elastic properties of the Si crystal yielding a fourfold symmetry along the ͓001͔ direction. 9,10 To understand these capped islands, cross-sectional TEM ͑XTEM͒ investigations were carried out. Figure 2 is XTEM images of GeSi islands capped with Si with different thicknesses.…”