Free Access
Microsc. Microanal. Microstruct.
Volume 6, Number 5-6, October / December 1995
Page(s) 465 - 472
Microsc. Microanal. Microstruct. 6, 465-472 (1995)
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 Tapfer1

1  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

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