IN0.2GA0.8AS GAAS INTERFACE REVEALED BY AN ALAS MARKER LAYER/

A detailed analysis of the microstructure of layered semiconductor het erostructures is only possible if the interface between the various la yers can be accurately located. Microstructural features whose charact erisation is dependent on the location of the interface include the pl anarity and width of the layers, the composition profile and the geome try of misfit dislocations (in the particular case of lattice mismatch ed heterostructures). We report on an investigation to image, at high resolution in the transmission electron microscope, the interface in a n In0.2Ga0.8As/GaAs structure grown by molecular beam epitaxy. The dif ficulty in locating the interface, due to similarity in electron optic al behaviour of GaAs and In0.2Ga0.8As when imaged in a [110] direction , was overcome by incorporating into the structure a ''marker layer'' of AlAs two unit cells thick (11.4 angstrom in total) between the GaAs and the In0.2Ga0.8As layers. Lattice fringe images of an In0.2Ga0.8As /AlAs/GaAs structure are presented which show, at near atomic resoluti on, the location of the misfit dislocations relative to the In0.2Ga0.8 As/GaAs interface.