GeSi intermixing in Ge nanostructures on Si(111): An XAFS versus STM study

Abstract

We report a detailed investigation of interdiffusion processes that occur during the growth of germanium nanostructures on the (111)-oriented surface of silicon. In particular, X-ray Absorption Fine Structure (XAFS) measurements performed ex situ show that a Ge(1-x)Si(x) alloy forms during deposition, with average composition x varying between 0.25 and 0.50, depending on substrate temperature and total coverage. By fitting the Si nearest-neighbor numbers around Ge as a function of the deposited thickness with a simple model, the effective vertical composition profile in the growth direction has been estimated. The latter has been described with a static effective diffusion length of (10.0 +/- 1.5) nm at 530 degrees C and (5 +/- 1) nm at 450 degrees C, which is interpreted as the dominance of surface transport processes in the intermixing dynamics. The analysis of the data on Ge-Ge bond length indicates a decrease of the Ge-Ge atomic distances with increasing Ge fraction, confirming previous theoretical predictions for strained epilayers. The XAFS results are compared to morphological information obtained by scanning tunneling microscopy investigations carried out in situ, yielding a satisfactory description for the epitaxy of this system

Strain-induced Ge segregation on Si at high temperatures

“…The Ge wetting layer obtained at high temperatures is of 2-3 bilayers thick [1,[3][4][5]. It is composed of SiGe with the Ge content reduced to about 70 and 50% according to EDX [3,35] and XAFS [36] data, respectively, due to Ge diffusion to the 3-D islands [3] and Ge-Si intermixing. The STM images obtained in this study have shown that the flat areas on the island and ridges top have preferably the 7 Â 7 reconstruction with small domains of the 5 Â 5 reconstruction.…”

“…The study of the Ge-Si composition is successfully carried out with several experimental methods [36]. It has been found that the GeSi intermixing leads to the complicated composition distribution in the Ge/Si bulk and at the interfaces [36,39,[45][46][47].…”

Low-dimensional systems investigated by x-ray absorption spectroscopy: a selection of 2D, 1D and 0D cases

“…Another extensive study on Ge nanostructures has been performed by Boscherini and co-workers [844][845][846]. The local structure around Ge was probed by using Ge K-edge XAS to provide direct evidence for the presence of considerable Si-Ge intermixing in strained and unstrained Ge quantum dots deposited on Si(001) and Si(111) [844].…”

A robust method for processing scanning probe microscopy images and determining nanoobject position and dimensions

“…SPM image processing is essential not only to reduce image distortions but also to precisely and reproducibly determine object dimensions and position in the image. This is a key step to investigate nanoobject intrinsic properties and subtle interplay between nanoobjects and their surroundings (Bromann et al , 1996; Medeiros‐Ribeiro et al , 1998; Springholz et al , 1998; Gusev et al , 2000; Repp et al , 2000; Knorr et al , 2002; Silly et al , 2004a,b; Kulawik et al , 2005; Mantooth et al , 2007; Motta et al , 2007; Nanayakkara et al , 2007; Yokoyama et al , 2007). However, this task can be challenging and time consuming.…”