21 research outputs found
Evidence for Kinetic Limitations as a Controlling Factor of Ge Pyramid Formation: a Study of Structural Features of Ge/Si(001) Wetting Layer Formed by Ge Deposition at Room Temperature Followed by Annealing at 600 {\deg}C
The article presents an experimental study of an issue of whether the
formation of arrays of Ge quantum dots on the Si(001) surface is an equilibrium
process or it is kinetically controlled. We deposited Ge on Si(001) at the room
temperature and explored crystallization of the disordered Ge film as a result
of annealing at 600 {\deg}C. The experiment has demonstrated that the
Ge/Si(001) film formed in the conditions of an isolated system consists of the
standard patched wetting layer and large droplike clusters of Ge rather than of
huts or domes which appear when a film is grown in a flux of Ge atoms arriving
on its surface. We conclude that the growth of the pyramids appearing at
temperatures greater than 600 {\deg}C is controlled by kinetics rather than
thermodynamic equilibrium whereas the wetting layer is an equilibrium
structure.Comment: Accepted for publication in Nanoscale Research Letter
An initial phase of Ge hut array formation at low temperature on Si(001)
We report a direct STM observation of Ge hut array nucleation on the Si(001)
surface during ultrahigh vacuum molecular-beam epitaxy at 360C. Nuclei of
pyramids and wedges have been observed on the wetting layer MxN patches
starting from the coverage of about 5.1 \r{A} (~3.6 ML). Further development of
hut arrays consists in simultaneous growth of the formerly appeared clusters
and nucleation of new ones resulting in gradual rise of hut number density with
increasing surface coverage. Huts nucleate reconstructing the patch surface
from the usual c(4x2) or p(2x2) structure to one of two recently described
formations composed by epitaxially oriented Ge dimer pairs and chains of four
dimers.Comment: Extended discussion; to appear in J. Appl. Phys., 201
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
Evolution of Ge wetting layers growing on smooth and rough Si (001) surfaces: isolated {105} facets as a kinetic factor of stress relaxation
The results of STM and RHEED studies of a thin Ge film grown on the
Si/Si(001) epitaxial layers with different surface relief are presented.
Process of the partial stress relaxation was accompanied by changes in the
surface structure of the Ge wetting layer. Besides the well-known sequence of
surface reconstructions ( patches) and hut clusters faceted with {105} planes, the formation of
isolated {105} planes, which faceted the edges of patches, has
been observed owing to the deposition of Ge on a rough Si/Si (001) surface. A
model of the isolated {105} facet formation has been proposed based on the
assumption that the mutual arrangement of the monoatomic steps on the initial
Si surface promotes the wetting layer formation with the inhomogeneously
distributed thickness that results in the appearance of patches
partially surrounded by deeper trenches than those observed in the usual Ge
wetting layer grown on the smooth Si(001) surface. Isolated {105} facets are an
inherent part of the Ge wetting layer structure and their formation decreases
the surface energy of the Ge wetting layer.Comment: 27 pages, 8 figure
Ge quantum dot arrays grown by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface: nucleation, morphology and CMOS compatibility
Issues of morphology, nucleation and growth of Ge cluster arrays deposited by
ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered.
Difference in nucleation of quantum dots during Ge deposition at low (<600 deg
C) and high (>600 deg. C) temperatures is studied by high resolution scanning
tunneling microscopy. The atomic models of growth of both species of Ge
huts---pyramids and wedges---are proposed. The growth cycle of Ge QD arrays at
low temperatures is explored. A problem of lowering of the array formation
temperature is discussed with the focus on CMOS compatibility of the entire
process; a special attention is paid upon approaches to reduction of treatment
temperature during the Si(001) surface pre-growth cleaning, which is at once a
key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array
formation process. The temperature of the Si clean surface preparation, the
final high-temperature step of which is, as a rule, carried out directly in the
MBE chamber just before the structure deposition, determines the compatibility
of formation process of Ge-QD-array based devices with the CMOS manufacturing
cycle. Silicon surface hydrogenation at the final stage of its wet chemical
etching during the preliminary cleaning is proposed as a possible way of
efficient reduction of the Si wafer pre-growth annealing temperature.Comment: 30 pages, 11 figure
STM and RHEED study of the Si(001)-c(8x8) surface
The Si(001) surface deoxidized by short annealing at T~925C in the ultrahigh
vacuum molecular beam epitaxy chamber has been in situ investigated by high
resolution scanning tunnelling microscopy (STM) and reflected high energy
electron diffraction (RHEED). RHEED patterns corresponding to (2x1) and (4x4)
structures were observed during sample treatment. The (4x4) reconstruction
arose at T<600C after annealing. The reconstruction was observed to be
reversible: the (4x4) structure turned into the (2x1) one at T>600C, the (4x4)
structure appeared again at recurring cooling. The c(8x8) reconstruction was
revealed by STM at room temperature on the same samples. A fraction of the
surface area covered by the c(8x8) structure decreased as the sample cooling
rate was reduced. The (2x1) structure was observed on the surface free of the
c(8x8) one. The c(8x8) structure has been evidenced to manifest itself as the
(4x4) one in the RHEED patterns. A model of the c(8x8) structure formation has
been built on the basis of the STM data. Origin of the high-order structure on
the Si(001) surface and its connection with the epinucleation phenomenon are
discussed.Comment: 26 pages, 12 figure