CHARACTERIZATION OF MBE GROWN SI/GEXSI1-X STRAINED LAYER SUPERLATTICES

The physical properties of both single Ge//xSi//1// minus //x epilayers and Ge//xSi//1// minus //x/Si strained layer superlattices (SLS's) grown by MBE on Si(100) substrates have been investigated. Raman scattering studies of Si/Ge//xSi//1// minus //x superlattices of period d equals d//S//i plus d//G//e//(//x//)//S//i//(//1// minus //x, with 17 less than equivalent to d less than equivalent to 65 nm, 10 less than equivalent to d//S//i less than equivalent to 45 nm, 4 less than equivalent to d//G//e//(//x//)//S//i//(//1// minus //x//) less than equivalent to 20 nm and 0. 2 less than equivalent to x less than equivalent to 0. 5, revealed low-frequency Raman lines associated with zone-folded acoustic phonons. The frequency shifts of optic phonons in SLS's compared with bulk alloys were used to reveal the strain distribution and composition of Ge//xSi//1// minus //x epilayers. Specific phonon features are observed in the alloy spectra that are attributed to Si-Ge ordering. Crystalline perfection and interface abruptness were assessed using cross-sectional transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS) and Rutherford backscattering spectrometry (RBS). The compositional uniformity, the strain tensor and superlattice periodicity were evaluated using x-ray diffraction.