Determination of the Order Parameter by Quantitative TEM Techniques

To quantitatively measure the order parameter in ordered III-V materials we have developed two techniques based on electron microscopy. The first technique calculates the diffraction pattern of ordered material quantitatively and fits the calculated data to experimentally obtained data. A test sample, specifically grown for this technique, shows that the method can determine the average order parameter with high accuracy. We found an order parameter of 0.34, which coincides with the value found by piezo-reflectance measurements. To measure the order parameter on a smaller length scale, we use a technique based on image processing of high-resolution TEM images. By comparing ordered and disordered parts of the image, we calculate the relative order parameter on an atomic length scale. Analyzing the data provides information about the development of the ordering in the crystal.