Single-crystal Sn/Ge superlattices on Ge substrates: Growth and structural properties

Short-period strained-layer alpha-Sn/Ge superlattices lattice matched to Ge(001) substrates have been synthesized for the first time. The thin, tetragonally distorted alpha-Sn layers are stabilized by a modified molecular beam epitaxy technique with large modulation of substrate temperature during growth. Optimization of growth conditions is achieved via in situ Auger electron spectroscopy and low-energy electron diffraction. This new kind of strained-layer superlattice is characterized by transmission electron microscopy, x-ray diffraction, and Raman scattering. Distinct superlattice effects are observed in the structural and phonon properties of the samples

Improvement of structural properties of Si/Ge superlattices

Short-period Si/Ge strained-layer superlattices are grown by molecular beam epitaxy (MBE) on Si(100) and Ge(100) substrates. Low-energy electron diffraction and Auger electron spectroscopy are performed between growth intervals, to obtain structural and compositional information. Raman spectroscopy and transmission electron microscopy are used for ex-situ characterization. Different buffer layers, varying in thickness and composition, are investigated to minimize the defect density in a symmetrically strained Si/Ge superlattice and to optimize the superlattice quality for various strain adjustments. The maximum thickness for two-dimensional and lattice-matched growth of the individual silicon and germanium layers on a strain-symmetrizing buffer are discussed. In addition, the thermal stability of short-period Si/Ge superlattices is studied as a function of strain distribution

Fabrication and properties of epitaxially stabilized Ge / α-Sn heterostructures on Ge(001)

We have investigated the influence of the growth parameters during molecular beam epitaxy on the realizibility of diamond crystal structure Ge / α-Sn alloys and superlattices on Ge(001) substrates. The segregation behaviour of Sn during Ge overgrowth has been studied. We find that for growth temperatures higher than 300°C the incorporation rates are less than 0.005 ML-1. The low-energy electron diffraction data of a series of Ge0.9Sn0.1 films deposited at substrate temperatures in the range of 185 to 275°C indicate a transition to amorphous growth for thicknesses beyond 20 Å. Single-crystal GenSnm superlattices with α-Sn layer thicknesses m of 1 and 2 monolayers and periodicities n + m between 10 and 22 monolayers have been fabricated by an unconventional molecular beam epitaxy technique which involves large substrate temperature modulations during growth. Structural characterization of the samples by means of transmission electron microscopy. Raman spectroscopy and X-ray diffraction exhibits distinct superlattice effects. The downward shift of the fundamental energy gap of the superlattices with increasing Sn content, as extracted from absorption measurents with a Fourier transform spectrometer, is in excellent agreement with theoretical values obtained from pseudopotential band structure calculations. The films were found to be stable against phase transition up to temperatures of 430–465°C, depending on the average Sn content