Highly spatially resolved X-ray analysis of semiconductor alloys and nanostructures in a scanning transmission electron microscope

Abstract
X-ray analysis in a high-resolution scanning transmission electron microscope is carried out on III-V compound and SixGe1-x, quantum wells and quantum wires. Simulated X-ray profiles were obtained by convolving the electron beam profile with a composition function. From best fits with experimental data, quantitated composition profiles can be obtained with nanometre resolution. Compositions in wells and wires are inhomogeneous. Alloy clusters tend to form in III-V compound quaternary quantum well stacks. SixGe1-x quantum wells on patterned substrates show strong compositional asymmetries along the growth direction and so do quantum wires in both materials systems. In the case of the SixGe1-x, system, aspects of the growth dynamics which lead to the observed compositional behaviour are deduced.