ELECTRON CHANNELING CONTRAST IMAGING OF INTERFACIAL DEFECTS IN STRAINED SILICON-GERMANIUM LAYERS ON SILICON

Images of defects at interfaces of strained Si1-xGex epilayers grown on bulk Si (001) substrates have been formed using the electron channelling contrast technique. The channelling images were obtained from bulk specimens using a highly efficient back scattered electron detector in an otherwise conventional scanning electron microscope equipped with a LaB, electron source. Good channelling contrast was observed despite the defects in some cases being over 1 mum below the specimen surface. The spatial resolution was found to be too low to distinguish individual dislocations known to be grouped in closely spaced clusters. Instead the images show the distribution of these dislocation clusters. Contrast variations other than those explained by g.b = g.b x u = 0 criteria were found. Image simulations confirmed the experimental observation that image contrast is stronger whilst the incident beam is close to the perpendicular to the dislocation line direction. The technique is excellent at showing the distribution of interface defects over large areas at a glance.