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CBED an Si-Ge Nanostrukturen

English title CBED on Si-Ge nanostructures
Applicant Müller Gubler Elisabeth
Number 103929
Funding scheme Project funding
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Condensed Matter Physics
Start/End 01.09.2004 - 30.04.2008
Approved amount 157'658.00
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Keywords (11)

CBED; TEM; SI-GE-C NANOSTRUCTURES; SI MBE; GE QUANTUM DOTS; QUANTUM CASCADE STRUCTURES; transmission electron microscopy; convergent beam electron diffraction; finite element calculation; elasticity theory; Si/SiGe multi quantum well structure

Lay Summary (English)

Lay summary
Lead:The local material composition has a strong impact on the physical properties of multi-phase semiconductor material. This project aims at an experimental determination of the local material composition by convergent beam electron diffraction and finite element calculations. As a model system a set of SiGe layers separated by Si spacer layers on Si(001) substrate is used.Background:In semiconductor nanostructures several crystal layers of different composition are grown on top of each other. For the physical properties of these materials it is of high importance, whether the interfaces are abrupt or whether the atomic species have interdiffused. Unfortunately, the real composition often differs from what was intended to be grown. It is, therefore, necessary to experimentally determine the local composition, in order to better understand the properties of the material as well as to get information, in what respect the material growth has to be change in order to improve the properties. It is usually difficult or even impossible to directly measure the local material composition. It may, however, be possible, to the deduce the composition, if the local lattice parameters are known. Convergent beam electron diffraction is a method, which is very suitable to experimentally determine the lattice parameters of a small area: in a transmission electron microscope a highly focussed beam is positioned at a certain point of the thin sample material. While for a plane wave of incident electrons a set of diffraction spots will be observed in the diffraction plane (i.e. the back focal plane of the objective lens), the spots will become disks in the case of a focussed beam. Within the diffraction disk of the undiffracted beam a number of dark lines is usually recognizable. From the arrangement of these lines the (three-dimensional) lattice parameters of the material can be deduced for the respective crystal area. If the elastic constants of the material are known, these can be used to determine on the basis of elasticity theory the local composition of the material from these local lattice parameters.Since such multi-phase material is usually heavily strained due to the different lattice parameters of the different materials, elastic relaxation has to be taken into account in the case of a thin electron microscopy specimens. In order to judge the effect of the elastic relaxation, finite element calculations are applied.Aim:The aim of this project is, to experimentally determine the local lattice parameters of the sample material and to deduce from these the local material composition using elasticity theory.Importance of the project:A method shall be developed, which allows the determination of the local material composition in nanostructured semiconductor material. This method is expected to contribute to an improvement in material synthesis for these complicated artificial materials which are expected to have very specific properties.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants


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Associated projects

Number Title Start Funding scheme
149294 Tensile strained Ge laser for Si-based opto-electronics 01.10.2013 Project funding
130181 Tensile strained Ge laser for Si-based opto-electronics 01.06.2010 Project funding