Short-period Si/SiGe strained-layer superlattices have been grown on bulk single-crystal SiGe substrates using a commercial low-temperature ultrahigh vacuum chemical vapor deposition reactor. The same structures were simultaneously grown on Si substrates for comparison. The materials were characterized by high-resolution X-ray diffraction (HRXRD), Auger electron spectroscopy (AES), atomic force microscopy (AFM), cross-sectional transmission electron microscopy (XTEM) and photoluminescence (PL). HRXRD, AES, and XTEM results show that the materials are high crystal-quality superlattice layers with abrupt interfaces as well as thickness and composition uniformity across superlattices of 5 periods. AFM images are consistent showing smooth surfaces with rms roughnesses much less than 1 nm for both the top layer and starting substrate surfaces. The low temperature PL spectra, which provide additional information about material quality and composition, show sharp, well-resolved near band-edge bound and free exciton lines and an intense broad sub-gap signal possibly related to superlattice transitions.
Journal of Crystal Growth253, no. June (4 April 2003): 77–84.