STRAIN AND DEFECTS IN SI/GE SUPERLATTICES FABRICATED ON A SI SUBSTRATE

Microstructures of MBE-grown Si12/Ge4 and Si18/Ge6 strained-layer superlattices (SLSs) were investigated using transmission electron microscopy and X-ray diffraction. Results showed that while the Ge/Si interfaces were flat and abrupt, the Si/Ge interfaces were neither flat nor distinct. In a plan-view image, dislocations in the Si substrate regarded as 60 degree type running along the orthogonal [110] directions were observed. V-shaped misfit islands were observed in the Si18/Ge6 SLS, but almost not in the Si12/Ge4 SLS. Shrinkage of the SLSs along the c axis from the ideal SLS due to their expanding along the a and b axes caused by the misfit dislocations was detected using X-ray diffraction.