18 research outputs found
Atomic structure of Ge quantum dots on the Si(001) surface
In situ morphological investigation of the {105} faceted Ge islands on the
Si(001) surface (hut clusters) have been carried out using an ultra high vacuum
instrument integrating a high resolution scanning tunnelling microscope and a
molecular beam epitaxy vessel. Both species of hut clusters--pyramids and
wedges--were found to have the same structure of the {105} facets which was
visualized. Structures of vertexes of the pyramidal clusters and ridges of the
wedge-shaped clusters were revealed as well and found to be different. This
allowed us to propose a crystallographic model of the {105} facets as well as
models of the atomic structure of both species of the hut clusters. An
inference is made that transitions between the cluster shapes are impossible.Comment: 6 pages, 6 figures. Accepted to JETP Letters (publication date
2010-03-25
Nucleation of Ge clusters at high temperatures on Ge/Si(001) wetting layer
Difference in nucleation of Ge quantum dots during Ge deposition at low (<
600C) and high (> 600C) temperatures on the Si(001) surface is studied by high
resolution scanning tunneling microscopy. Two process resulting in appearance
of {105}-faceted clusters on the Ge wetting layer have been observed at high
temperatures: Pyramids have been observed to nucleate via the previously
described formation of strictly determined structures, resembling blossoms,
composed by 16 dimers grouped in pairs and chains of 4 dimes on tops of the
wetting layer M x N patches, each on top of a separate single patch, just like
it goes on at low temperatures; an alternative process consists in faceting of
shapeless heaps of excess Ge atoms which arise in the vicinity of strong sinks
of adatoms, such as pits or steps. The latter process has never been observed
at low temperatures; it is typical only for the high-temperature deposition
mode.Comment: 13 pages, 4 figures; a revised versio
Application of hydrogenation to low-temperature cleaning of the Si(001) surface in the processes of molecular-beam epitaxy: Investigation by STM, RHEED and HRTEM
Structural properties of the clean Si(001) surface obtained as a result of
low-temperature (470--650C) pre-growth annealings of silicon wafers in a
molecular-beam epitaxy chamber have been investigated. To decrease the cleaning
temperature, a silicon surface was hydrogenated in the process of a preliminary
chemical treatment in HF and NH_4F aqueous solutions. It has been shown that
smooth surfaces composed by wide terraces separated by monoatomic steps can be
obtained by dehydrogenation at the temperatures > 600C, whereas clean surfaces
obtained at the temperatures < 600C are rough. It has been found that there
exists a dependence of structural properties of clean surfaces on the
temperature of hydrogen thermal desorption and the process of the preliminary
chemical treatment. The frequency of detachment/attachment of Si dimers from/to
the steps and effect of the Ehrlich-Schwoebel barrier on ad-dimer migration
across steps have been found to be the most probable factors determining a
degree of the resultant surface roughness.Comment: 8 pages, 8 figures; version accepted to J. Appl. Phy
Absorption of Terahertz Radiation in Ge/Si(001) Heterostructures with Quantum Dots
The terahertz spectra of the dynamic conductivity and radiation absorption
coefficient in germanium-silicon heterostructures with arrays of Ge hut
clusters (quantum dots) have been measured for the first time in the frequency
range of 0.3-1.2 THz at room temperature. It has been found that the effective
dynamic conductivity and effective radiation absorption coefficient in the
heterostructure due to the presence of germanium quantum dots in it are much
larger than the respective quantities of both the bulk Ge single crystal and
Ge/Si(001) without arrays of quantum dots. The possible microscopic mechanisms
of the detected increase in the absorption in arrays of quantum dots have been
discussed.Comment: 9 pages, 4 figures; typos correcte