Characterization of MBE grown Si/Ge xSi 1−x strained layer superlattices

Abstract

The physical properties of both single Ge xSi 1−x epilayers and Ge xSi 1−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−x superlattices of period d = d Si + d Ge x Si 1− x , with 17 ⩽ d ⩽ 65 nm, 10 ⩽ d Si ⩽ 45 nm, 4 ⩽ d Ge xSi 1−x ⩽ 20 nm and 0.2 ⩽ × ⩽ 0.5, revealed a series of 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−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). In addition, the compositional uniformity, the strain tensor and superlattice periodicity were evaluated using X-ray diffraction.