Top Ge Layer Research Articles

Morphological and compositional evolution of the ge/si(001) surface during exposure to a si flux.

By using scanning tunneling microscopy we found that the surface reconstruction of Ge/Si(001) epilayers evolves from (M x N) to (2 x N), and eventually to (2 x 1), during exposure to a Si flux. This sequence appears to be just the inverse of that observed during the growth of Ge or SiGe alloys on Si(001). However, molecular dynamics simulations supported by ab initio calculations allow us to interpret this morphological evolution in terms of Si migration through the epilayer and complex Si-Ge intermixing below the top Ge layer.

X-ray evidence for Ge/Si(0 0 1) island columns in multilayer structure

A Ge/Si(0 0 1) multilayer structure is investigated by cross-sectional transmission electron microscopy, atomic force microscopy and double crystal X-ray diffraction. We find that the multilayer-structure-related satellite peaks in the rocking curve exhibit a similar nonuniform broadening and we fit the zero-order peak with two Lorentz lineshapes. The ratio of the integrated intensity of two peaks is approximately equal with the areal ratio of the top Ge layer deposited between the areas that are and are not occupied by islands. It proves the existence of vertical-aligned island columns from the viewpoint of macroscopic dimension.

Quantum Dot Growth in the Si-Ge-C System Through Multi-Step Procedure

ABSTRACTTo fabricate nanometer-sized Ge dots on Si(100), we have investigated multi-step procedure, involving low temperature deposition of a Ge layer, a sub-monolayer C on a Ge wetting layer, a Ge top layer for three-dimensional (3D) dot formation and post-annealing. Effects of each procedure were discussed on the basis of an atomic force microscope study. 10nm-sized Ge dots with a high number density in the order of 1011 cm−2 were grown on the Si(100) substrate by combining each procedure and optimizing experimental conditions, such as deposition temperature, the C layer thickness and post-annealing temperature.

Atomic bond configuration of Ge(111)-( sqrt 3 x sqrt 3 )R30 degrees-Au: A low-energy electron-diffraction study.

We determined the bond geometry of the Ge(111)-(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{}-Au surface by means of low-energy electron diffraction. The resulting lateral parameters are in excellent agreement with values recently obtained by a surface x-ray-diffraction study while perpendicular parameters differ substantially from them. The Au/Ge(111)-(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} surface consists of a (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} net of Au atoms which replace the topmost Ge atoms and form trimers. The Au-Au bond length is 2.81\ifmmode\pm\else\textpm\fi{}0.07 \AA{}. The Ge atoms in the second layer are laterally displaced from their bulk positions by 0.5 \AA{}, resulting in a Au-Ge bond length of 2.50\ifmmode\pm\else\textpm\fi{}0.14 \AA{}. The missing top Ge layer and the displacement of second-layer Ge atoms lead to distortions in deeper Ge layers, most notably a buckling in the third and fourth Ge layers with a magnitude of about 0.2 \AA{}.

Raman scattering in Ge-Ge1-xSix superlattice

Raman studies of Ge based Ge1-xSix superlattices are presented. Using Raman spectroscopy as a local probe, only the first Ge-Ge1-xSix bilayer underneath the surface is explored. It is shown that the top Ge layer experiences a biaxial elastic stress which we evaluate. The silicon content of the Ge1-xSix layer is deduced from the peak frequency of both Ge-Ge and Ge-Si bond vibrations. The Ge-Ge1-xSix interfacial perfection is also investigated. The Raman data reveal a smearing of this heteroboundary.

Gold-induced germanium crystallization.

When in contact with metal, amorphous silicon (a-Si) or germanium (a-Ge) often crystallize at temperatures significantly lower than in their bulk form. In order to understand the role of the contact metal, we have studied the crystallization process of a-Ge/Au bilayers and codeposited a-${\mathrm{Ge}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Au}}_{\mathit{x}}$ films (x=0.04 and 0.22) by measuring the Ge and Au extended x-ray-absorption fine structure. Upon isothermal annealing, the Ge/Au bilayer crystallizes at 170 \ifmmode^\circ\else\textdegree\fi{}C, and concomitantly, a large amount of Au migrates into the Ge top layer. For codeposited films, the x=0.22 sample crystallizes at 130 \ifmmode^\circ\else\textdegree\fi{}C and the x=0.04 sample at 330 \ifmmode^\circ\else\textdegree\fi{}C. In the amorphous x=0.04 and 0.22 films, each Au atom on the average is bound with one to two Ge atoms at 2.4 \AA{}, but does not have Au neighbors. As the films crystallize, Au transforms into fcc gold in the x=0.22 sample but remains bound with Ge in the x=0.04 sample. Our results demonstrate that Au-Ge bonding is significant in the a-Ge and may play an important role in lowering the Ge crystallization temperature.

Evolution of Epitaxial SixGei1-x Alloys on Si(100) During Thermal Annealing a-Ge/Au Bilayers Deposited on Si Substrate

ABSTRACTSolid phase epitaxial (SPE) growth of SixGei1-x alloys on Si (100) was achieved by thermal annealing a-Ge/Au bilayers deposited on single crystal Si substrate in the temperature range of 280°C to 310°C. Growth dynamics was investigated using X-ray diffraction, Rutherford backscattering spectrometry, and cross-sectional transmission electron microscopy. Upon annealing, Ge atoms migrate along the grain boundaries of polycrystalline Au and the epitaxial growth initiates at localized triple points between two Au grains and Si substrate, simultaneously incorporating a small amount of Si dissolved in Au. The Au is gradually displaced into the top Ge layer. Individual single crystal SixGei1-x islands then grow laterally as well as vertically. Finally, the islands coalesce to form a uniform layer of epitaxial SixGe1-x alloy on the Si substrate. The amount of Si incorporated in the final epitaxial film was found to be dependent upon the annealing temperature.