Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

Chapter 8
Conclusions
In summary, self-assembled MBE growth of InAs and InGaAs QDs on at Si(100)
has been intensively studied. Reection high energy diraction (RHEED) streak
patterns conrm that the combination of the atomic hydrogen followed by thermal
desorption is an ecient surface cleaning method. An additional improvement
for the cleaning and growth is achieved by exposing the Si surface with Ga at low
uxes resulted in a strong reduction of the lateral size of InAs QDs from 50-70 nm
down to 25-30 nm and a signicant enhancement of the homogeneity of the dot
size and distribution. The evolution of size, density and shape of the QDs are exsitu
characterized by AFM and TEM. Dierent growth parameters such as InAs
coverage, growth temperature, In-growth rate and V/III ratio are examined on
dierently prepared silicon surfaces. The InAs QDs density is strongly increased
from 10 8 to 10 11 cm −2 at V/III ratios in the range of 15-35 (beam equivalent
pressure values). InAs QD formations are not observed at temperatures as high
as 500 ◦ C. Moreover, InAs quantum dashes are observed on at higher In-growth
rate of 0.3 ML/s.
TEM characterizations of InAs QDs embedded in silicon matrix with dierent
nominal thicknesses on dierent o-cuts substrates showed semi-coherent QDs
with good crystal quality inside the dots and mist dislocations at the interface of
InAs/Si. The substrate ocut found to have inuence on the QDs shape and geometry.
A very homogeneous narrow QDs size with D= 5-8 nm distribution with
spherical to multi-facet shape has been observed on ocut substrate, compared
to a broader size distribution with D= 15-25 nm observed on exactly oriented
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