Initial stage growth of GexSi1?x layers and Ge quantum dot formation on GexSi1?x surface by MBE

Critical thicknesses of two-dimensional to three-dimensional growth in Ge_xSi_1−x layers were measured as a function of composition for different growth temperatures. In addition to the (2 × 1) superstructure for a Ge film grown on Si(100), the Ge_xSi_1−x layers are characterized by the formation of (2 × n) reconstruction. We measured n for all layers of Ge/Ge_xSi_1−x/Ge heterosystem using our software with respect to the video recording of reflection high-energy electron diffraction (RHEED) pattern during growth. The n reaches a minimum value of about 8 for clear Ge layer, whereas for Ge_xSi_1−x films, n is increased from 8 to 14. The presence of a thin strained film of the Ge_xSi_1−x caused not only the changes in critical thicknesses of the transitions, but also affected the properties of the germanium nanocluster array for the top Ge layer. Based on the RHEED data, the hut-like island form, which has not been previously observed by us between the hut and dome islands, has been detected. Data on the growth of Ge/Ge_xSi_1−x/Ge heterostructures with the uniform array of islands in the second layer of the Ge film have been received.     

Causes of the stability of three-bilayer islands and steps on a Si (111) surface

The initial stages of growth of Ge and Si layers on a singular Si (111) surface result in an unusual morphology of the growth surface if the layers are deposited at a low rate; i.e., triangular islands with a height of as much as three atomic layers are formed. A simulation based on the Monte Carlo method has been used to show that an additional barrier with a height of 0.5–0.6 eV, serving to incorporate atoms into dimerized bonds at the edges of the triangular islands, brings about enhanced growth of the islands in relation to their height and a change in the triangles’ orientation. According to the suggested hypothesis, the increase in the islands’ height and the limitation of their height to three bilayers are due to the effect of the edge dimers, whose orientation changes when the height of a step perpendicular to the \(\langle \bar 1\bar 12\rangle \) direction becomes as large as three bilayers. Scanning tunneling microscopy has been used to detect new special features in the atomic structure of regular three-bilayer steps on a Si (557) surface. The results of an analysis of the images obtained using a scanning tunneling microscope confirm the hypothesis that a row of dimers is formed at the edge of a three-bilayer step.     

Study of initial stages of Pb growth on the Si (7710) surface by the method of scanning tunneling spectroscopy

Lead island growth on the Si (7710) surface containing steps three interplanar spacings d ₍₁₁₁₎ in height and on the Si (111) singular surface was studied by scanning tunneling microscopy at room temperature. It is shown that triple steps control the shape and orientation of lead islands formed on the Si (7710) surface. It was found that preliminary storage of a silicon sample in a vacuum chamber affects the size and density of growing islands. According to the Auger electron spectroscopy data, this effect is caused by oxygen adsorption on the substrate surface from the residual atmosphere of the vacuum chamber.     

Tunneling transport through passivated CdS nanocrystal arrays grown by the Langmuir-Blodgett method

Tunneling electron transport through CdS nanocrystal arrays fabricated by the Langmuir-Blodgett method are studied by scanning electron spectroscopy. The effect of the matrix-annealing atmosphere on tunneling transport through the nanocrystal arrays is studied. Electron capture at traps in the case of nanocrystals annealed in vacuum is detected by tunneling current-voltage characteristics analyzed using a model relating the data of tunneling spectroscopy, photoluminescence, and quantum-mechanical calculation. Analysis shows that the nanocrystal surface is passivated by an ammonia monolayer upon annealing in an ammonia atmosphere. It is found that the substrate and surrounding non-passivated nanocrystals have an effect on the electron polarization energy.     

Ge and GexSi1 − x islands formation on GexSi1 − x solid solution surface

Critical thicknesses of 2D to 3D growth and morphological ‘hut’-‘dome’ cluster transitions in Ge layers were measured. In comparison with the growth on the pure Si(100) surface, a decrease in the critical thicknesses of 2D-3D and hut-dome transitions was observed and accounted for by the accumulation of elastic strains as Ge content or thickness of the GeSi solid solution increased. The density and size of Ge nanoclusters were determined depending on the solid solution composition. The presence of a thin strained layer of the GeSi solid solution caused not only the changes in critical thicknesses of the transitions, but also affected the properties of the germanium nanocluster array.     

An Unusual Mechanism of Misfit Stress Relaxation in Thin Nanofilms

Technical Physics Letters - A new mechanism of misfit stress relaxation in nanofilms with variable density of surface phases is established. This phenomenon is ensured by ordered mass transfer of...     

Formation of Ge/Si and Ge/Ge x Si1−x /Si nanoheterostructures by molecular beam epitaxy

A kinetic diagram of Ge growth on Si is constructed by methods of fast electron diffraction and scanning electron microscopy. Activation energies of morphological transitions from two-dimensional to three-dimensional growth and from hut-clusters to dome-type islands are determined. The curve of the 2D–3D transition has two segments that follow the Arrhenius law and refer to different mechanisms of two-dimensional growth: two-dimensional island mechanism in the temperature range of 300–525 °C with the activation energy of ?0.11 eV and step motion in the temperature range of 525–700 °C with the activation energy of 0.15 eV. Transitions from hut-islands to dome-islands are also observed. The curve constructed for the hut-dome transition is approximated by two exponential segments that obey the Arrhenius law. The hut-dome transition activation energy is 0.11 eV in the temperature range of 350–550 °C and 0.24 eV in the temperature range of 550–700 °C. The maximum density of islands in the case of Ge growth on a Ge _x Si_1?x layer reaches 4 · 10¹¹ cm^?2. An increase in the composition leads to an increase in the density of Ge islands owing to a decrease in the length of migration of Ge adatoms on the Ge _x Si_1?x surface, as compared to the case of Ge growth on Si. The periodicity N, which is manifested as a (2 × N) superstructure, decreases during the reconstruction from 14 to 8 with increasing Ge content in the Ge _x Si_1?x layer. An increase in thickness or temperature leads to a decrease in periodicity and testifies to Ge segregation; in this case, stress relaxation occurs, which reduces the Ge diffisivity.