Composition determination in the GaAs/(Al, Ga)As system using contrast in dark-field transmission electron microscope images

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Abstract
The sensitivity to composition of transmission electron microscope images of (Al, Ga)As obtained using the 002 reflection is well known. Here we assess the potential quantitative use of such images for the compositional analysis of heterostructures and find that typical values of the composition parameter (x in AlxGa1−xAs) can in principle be determined to ±0·02, with unit-cell spatial resolution. A treatment is described which is simple to apply and which, although based on a kinematical approach, nonetheless takes account of the effects of dynamical scattering, inelastic scattering and a variety of other sources of error. The method and its limitations are demonstrated for a variety of technologically interesting structures. We note the further improvement in accuracy that is potentially achievable by the use of energy filtering.