Structural characterization of Si,Ge, strained layer superlattices

Si,Ge, strained layer superlattice (SLS) structures were grown by molecular beam epitaxy on Ge$ii --x buffer layers on (100) Si substrates to determine the effects of buffer layer composition, SLS thickness ratio, and superlattice periodicity, on the overall quality of these structures. X-ray diffraction methods were used to determine how closely actual periodicities and compositions met targeted values, and to evaluate the quality of these samples. In most instances the as-grown structures matched the targeted values to within lo%, though in some instances deviations of 20-25% in either the period or composition were observed. The quality of the SLS structures was greatly dependent on the composition of the buffer layer on which it was grown. Si,Ge, SLS structures grown on Siand Ge-rich buffer layers were of much higher quality than Si,Ge, SLSs grown on Ge O,soSio~so layers, but the x-ray rocking curves of the Si,Ge, samples indicated that they were far from perfect and contained moderate levels of defects. These results were confirmed by cross sectional transmission electron microscopy, which showed that the Si,Ge, structures contained significant numbers of dislocations and that the layers were nonuniform in thickness and wavy in appearance. Si,Ge, structures, however, displayed fewer defects but some dislocations and nonparallelism of layers were still observed,