Free Access
Microsc. Microanal. Microstruct.
Volume 6, Number 5-6, October / December 1995
Page(s) 473 - 482
Microsc. Microanal. Microstruct. 6, 473-482 (1995)
DOI: 10.1051/mmm:1995138

Strain Relaxation of Si/Ge Multilayers Investigated by Transmission Electron Microscopy and High-Resolution X-Ray Diffractometry

Elvio Carlino1, Cinzia Giannini1, Leander Tapfer1, Kurt A. Mäder2 et Hans von Känel2

1  PASTIS-Centro Nazionale Ricerca e Sviluppo Materiali (PASTIS-CNRSM) S.S. 7 Appia km. 712, 72100 Brindisi, Italy
2  Laboratorium für Festkörperphysics, ETH-Zürich, CH-8093, Switzerland

In this work we investigate the strain-relief mechanisms and the formation of structural defects of Si/Ge multilayers grown by molecular beam epitaxy on (100)- Si substrates. The investigated specimens differ in number of periods, period thickness, and in the Si/Ge layer thickness ratio. The structural analyses are performed by transmission electron microscopy and high-resolution X-ray diffraction. We found that a Si-Ge interdiffusion induces a broadening of the nominal thickness of the Ge layer, producing a $\rm Si_x Ge_{1-x}$ alloy as well as a higher Ge content in the last periods of the multilayer structure. Our measurements suggest that the strain relaxation occurs in two steps: i) in each period of the multilayer the strain energy density is partially reduced by the formation of coherent islands; ii) at a certain value of the strain energy density, the shape of the coherent islands changes and the structures, partially or completely, relax the accumulated strain energy by nucleation of dislocations. The increase of the strain energy density is related to the measured monotonic increase of the Ge content as a function of the growth time.

6865 - Low dimensional structures: growth, structure and nonelectronic properties.
6825 - Mechanical and acoustical properties of solid surfaces and interfaces.
6220F - Deformation and plasticity.
8140L - Deformation, plasticity and creep.
6822 - Surface diffusion, segregation and interfacial compound formation.
6170J - Etch pits, decoration, transmission electron microscopy and other direct observations of dislocations.

Key words
chemical interdiffusion -- deformation -- dislocation nucleation -- elemental semiconductors -- germanium -- semiconductor epitaxial layers -- semiconductor heterojunctions -- silicon -- transmission electron microscopy -- X ray diffraction -- multilayers -- high resolution X ray diffractometry -- TEM -- strain relief -- structural defects -- molecular beam epitaxy -- Si 100 substrates -- layer thickness ratio -- interdiffusion -- strain relaxation -- strain energy density -- coherent islands -- dislocation nucleation -- Ge content -- growth time -- semiconductors -- Si Ge -- SiGe -- Si

© EDP Sciences 1995