INTERFACIAL STUDIES IN SEMICONDUCTOR HETEROSTRUCTURES BY X-RAY-DIFFRACTION TECHNIQUES

X-ray radiation is a non-destructive probe well suited to assess struc tural perfection of semiconductor material. Three techniques are used to study the interfacial roughness, period fluctuations and annealing- induced interdiffusion in various superlattice structures. Reflectivit y of long period Si/Si1-xGex multiple quantum wells reveals an asymmet ry oriented along the direction of miscut in the interface roughness w ith the Si1-xGex to Si interfaces being about twice as rough (0.5 vers us 0.3 nm) as the Si to Si1-xGex interfaces. For Si-Si0.65Ge0.35 multi ple quantum wells, diffuse scattering is minimal for a growth temperat ure of 550 degrees C and increases substantially at very low (250 degr ees C) or high (750 degrees C) growth temperatures. In (SimGen)(p) sho rt period superlattices, the X-ray reflectivity data are consistent wi th interfacial mixing over about two monolayers and thickness fluctuat ions of about 5% vertically in the structures. For superlattices grown on vicinal surfaces, the roughness spectrum is correlated with the su rface miscut orientation. Double-crystal X-ray diffraction using symme trical and asymmetrical reflections has been used to study epitaxial l attice distortion and strain relaxation in InGaAs/GaAs heterostructure s grown on (100) on-orientation and 2 degrees off (100) GaAs surfaces. It is shown that thick InGaAs films retain an appreciable fraction of their initial strain and that their crystal lattice is triclinically distorted. The magnitude of the deformation is larger when growth is c arried out on a vicinal surface.