Transmission electron microscopy of short-period Si/Ge strained-layer superlattices on Ge substrates

Structural investigations of high quality Si/Ge strained-layer superlattices (SLSs) on [001] oriented Ge substrates prepared by molecular beam epitaxy are presented. Cross-sectional transmission electron microscopy reveals that a defect-free superlattice is achieved for a structure composed of a 20-period sequence of 3 monolayers (ML) Si and 9 ML Ge. High-resolution lattice images and electron diffraction patterns show that the whole structure is matched to the Ge substrate. Experimental values for the tetragonal deformation of the Si layers within the SLS are in good agreement with theory. An equivalent sample containing 120 periods exceeds the critical thickness for pseudomorphic growth of the SLS and shows the formation of twin lamellae. Applied Physics Letters is copyrighted by The American Institute of Physics

Symmetry properties of short period (001) Si/Ge superlattices

Depending on the composition of [001] oriented short period SimGen superlattices (m monolayers Si/n monolayers Ge) there are six different space groups. In case of m+n odd the microscopic periodicity is doubled to 2(m+n) monolayers due to the tetrahedral bonding. We prepared several superlattices namely Si2Ge3, Si3Ge3 and Si4Ge6 with low temperature molecular beam epitaxy. Using selected area diffraction in the transmission electron microscope we found the microscopic periodicity of 10 monolayers for Si2Ge3 and Si4Ge6. For Si3Ge3 the vertical periodicity is six monolayers

Novel relaxation process in strained Si/Ge superlattices grown on Ge (001)

A new mode of misfit defect formation has been observed for the first time in high quality Si/Ge strained-layer superlattices grown by molecular beam epitaxy on Ge(001). In order to investigate the transition from coherent to incoherent growth we have studied a set of samples with a varying number of superlattice periods by transmission electron microscopy. High-resolution lattice imaging reveals that strain relaxation occurs through successive glide of 90° (a/6) Shockley partial dislocations on adjacent {111} planes. The resulting microtwins represent the only relaxation mechanism we observed in the samples. Applied Physics Letters is copyrighted by The American Institute of Physics

Contrast investigations of surface acoustic waves by stroboscopic topography 3. Contrast in transmission case

Submitted to: Phys. Stat. Sol.SIGLETIB: RN 5581 (85-12) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Interfacial layers and their effect on leakage current in MOCVD-deposited SBT thin films

Strontium bismuth tantalate (SBT) thin films were deposited on Pt/Ti electrodes by metalorganic chemical vapor deposition (MOCVD). Interactions at the interface of Pt and SBT and their effect on leakage current were investigated. High-resolution transmission electron micrographs (HRTEM) reveal that after annealing at 700degreesC, a 1-2 nm thick interfacial layer built. Auger electron spectra (AES) confirm that the constituents of SBT intermix with the Pt and vice versa. Schottky emission yields a nice linear fit to the leakage current data but the extracted values of the optical dielectric constant and the Richardson constant do not meet experimental values. Taking into account an interfacial layer with low dielectric constant and the effect of diffusion on the Schottky emission these inconsistencies can be resolved