Eur. Phys. J. Special Topics 167, 41-46 (2009)
DOI: 10.1140/epjst/e2009-00934-7

X-ray diffraction study of the composition and strain fields in buried SiGe islands

N. Hrauda¹, J.J. Zhang¹, M. Stoffel², J. Stangl¹, G. Bauer¹, A. Rehman-Khan¹, V. Holý³, O.G. Schmidt², V. Jovanovic⁴ and L.K. Nanver<sup>4

1</sup>  Institute for Solid State and Semiconductor Physics, Johannes Kepler University of Linz, Altenbergerstrasse 69, 4040 Linz, Austria
²  IWF Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
³  Faculty of Mathematics and Physics, Charles University Prague, Ke Karlovu 5, Praha, 12116, Czech Republic
⁴  TU Delft, Stevinweg 1, 2628, The Netherlands

nina.hrauda@jku.at

Abstract
We report on studies of strain and composition of two-dimensionally ordered SiGe islands grown by molecular beam epitaxy using high resolution x-ray diffraction. To ensure a small size distribution of the islands, pit-patterned 4'' (001) Si wafers were used as substrates. The Si wafers were patterned by optical lithography and reactive ion etching. The pits for island growth are ordered in regular 2D arrays with periods ranging from 500 to 1000 nm along two orthogonal 110 directions. After the growth of a Si buffer layer, 5 to 9 monolayers of Ge are deposited, leading to the formation of islands with either dome- or barn shape, depending on the number of monolayers deposited. The Si capping of the islands is performed at low temperatures to avoid intermixing and thus strain relaxation. Information on the surface morphology obtained by atomic force microscopy (AFM) was used to set up models for three-dimensional Finite Element Method (FEM) simulations of the islands including the patterned Si substrate. In the model, special attention was given to the non uniform distribution of the Ge content within the islands. The FEM results served as an input for calculating the diffracted x-ray intensities using kinematical scattering theory. Reciprocal space maps around the vicinity of symmetric (004) and asymmetric (113) and (224) Bragg peaks were recorded in coplanar geometry. Simulating different germanium gradients leads to altered scattered intensity distribution and consequently information on this quantity is obtained for both dome- and barn-shaped islands as well as on the strain fields.

© EDP Sciences, Springer-Verlag 2009

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