X-ray diffraction study of the composition and strain fields in buried SiGe islands |
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Authors: | N Hrauda J J Zhang M Stoffel J Stangl G Bauer A Rehman-Khan V Holy O G Schmidt V Jovanovic and L K Nanver |
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Institution: | (1) 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, 12116 Praha, Czech Republic;(4) TU Delft, Stevinweg 1, 2628, Delft, The Netherlands |
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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 (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 (300○C) 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. |
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