The determination of the strain in GaAs/Gax In1-x As strained-layer structures from measurements of thickness fringe displacements

A. J. Harvey, D. A. Faux, U. Bangert, P. Charsley

Research output: Contribution to journalArticlepeer-review

Abstract

The initial stage in the development of a technique which has the aim of determining the misfit strain in structures containing strained layers is described. The method is applied to a GaAs system containing GaxIn1-xAs strained layers. Transmission electron microscopy images of the shifts in the thickness fringes in (100) epitaxial layers due to strain relaxation at the edge of 90° wedge samples are matched to simulated images obtained by calculating the strain relaxation and solving the equations for the two-beam dynamical theory of diffraction contrast. The simulated images are analysed as a function of the deviation parameter s, the misfit strain f, the g vector, the extinction coefficient ζg and the anomalous absorption coefficient ζg. The simulated images are sufficiently sensitive to f and to s that contrast patterns can be distinguished which differ by less than 0-02% in f and by about 1 × 10−4 Å−1 in s. The pattern of the image is not very sensitive to changes in ζg or ζg. Thus the pattern matching of experimental and simulated images leads to values of s and f only. The sensitivity both to s and to f is illustrated by examining a single strained Ga0·8In0·2As quantum well with GaAs barriers. The values for the misfit strain obtained are in good agreement with expected values from growth and photoluminescence measurements. The results also indicate a rotation of the cap with respect to the substrate and a slight relaxation of the strain due to misfit dislocations.

Original languageEnglish
Pages (from-to)433-446
Number of pages14
JournalPhilosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties
Volume67
Issue number2
DOIs
Publication statusPublished - Feb 1993

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