| Issue |
Microsc. Microanal. Microstruct.
Volume 6, Number 5-6, October / December 1995
|
|
|---|---|---|
| Page(s) | 465 - 472 | |
| DOI | https://doi.org/10.1051/mmm:1995137 | |
DOI: 10.1051/mmm:1995137
Elastic Stress Relaxation in HRTEM Specimens of Strained Semiconductor Heterostructures and its Influence on the Image Contrast
Liberato De Caro1, Antonino Giuffrida2, Elvio Carlino1 et Leander Tapfer11 PASTIS-Centro Nazionale Ricerca e Sviluppo Materiali (PASTIS-CNRSM), Strada Statale 7 Appia km 712, 72100 Brindisi, Italy
2 Università degli Studi di Lecce, Dipartimento di Fisica, via Arnesano, 73100 Lecce, Italy
Abstract
HRTEM observations require ultra-thinned specimens and, due to the very small
thickness (1 to
30 nm), an elastic stress relaxation may occur near the free surfaces of
strained heterostructures.
These relaxation phenomena can modify the structural features of the
thinned specimens with
respect to the bulk materials. Thus, the role of the relaxation has
to be taken into account if the
structural properties of the bulk heterostructures are deduced from
those of the thinned
specimens. In this work we investigate the case of lattice-mismatched
semiconductor
superlattices, thinned along the [011]-crystallographic direction. The
theoretical evaluation of
strain fields in ultra-thinned HRTEM samples shows a bending of the
lattice, and the local lattice
spacings are representative of neither the bulk tetragonally distorted
material nor the unstressed
material. Our results show that these distortions can be large and must
be taken into account
whenever HRTEM is used to deduce the local chemical composition or the
unit cell dimensions
in strained semiconductor materials.
6116D - Electron microscopy determinations of structures.
6865 - Low dimensional structures: growth, structure and nonelectronic properties.
6220 - Mechanical properties of solids related to microscopic structure.
8140J - Elasticity and anelasticity.
6825 - Mechanical and acoustical properties of solid surfaces and interfaces.
Key words
semiconductor superlattices -- stress relaxation -- transmission electron microscopy -- strained semiconductor heterostructures -- elastic stress relaxation -- HRTEM -- ultra thin specimens -- image contrast -- free surfaces -- lattice mismatched superlattices -- strain fields -- lattice spacings -- local chemical composition -- unit cell dimensions
© EDP Sciences 1995