High Resolution Z-Contrast Imaging of Semiconductor Interfaces

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Abstract
The structural and compositional integrity of interfaces between semiconductor multilayers can profoundly influence the optical and electronic properties of epitaxially grown heterostructures. Understanding the atomic-scale interfacial structure and chemistry is therefore essential to correctly relate electrical measurements to theoretical models and to correlate such effects with growth conditions. High-resolution electron microscopy (HREM) has played a pivotal role in this process, providing important information on interface commensurability and revealing the presence and nature of defects. More recently, significant advances have been made in applying HREM to the difficult problem of chemical composition mapping in systems where no structural change occurs across the interfaces. The basis of such methods involves using the objective lens as a bandpass filter and tuning in on a specific range of spatial frequencies to form a chemically sensitive interference pattern. By using a suitable low-index zone axis and choosing an optimum range of specimen thickness, the patterns can indeed be extremely sensitive to the strength and periodicities of the projected potential.