High-resolution electron holography for the study of composition and strain in thin film semiconductors

A method for simultaneous measurement of strain and composition in exactly the same specimen area is proposed using high-resolution electron holography. Results are shown for a strained semiconducting thin films consisting in a Si 0.7 Ge 0.3 layer epitaxially grown on a silicon substrate. Experiments were carried out using an aberration-corrected transmission electron microscope fitted with a field emission gun and electron biprism. We demonstrate the efficiency of the technique for providing accurate information on local chemical composition to 5% and strain to 0.1% at a spatial resolution of 2 nm. The accuracy of the results is discussed as are surface relaxation effects.