The main focus and concerns of this PhD thesis is the growth of III-V
semiconductor nanostructures (Quantum dots (QDs) and quantum
dashes) on silicon substrates using molecular beam epitaxy (MBE)
technique. The investigation of influence of the major growth parameters
on their basic properties (density, geometry, composition, size
etc.) and the systematic characterization of their structural and optical
properties are the core of the research work. The monolithic integration
of III-V optoelectronic devices with silicon electronic circuits
could bring enormous prospect for the existing semiconductor technology.
Our challenging approach is to combine the superior passive
optical properties of silicon with the superior optical emission properties
of III-V material by reducing the amount of III-V materials to
the very limit of the active region.
Different heteroepitaxial integration approaches have been investigated
to overcome the materials issues between III-V and Si. However,
this include the self-assembled growth of InAs and InGaAs QDs
in silicon and GaAx matrices directly on flat silicon substrate, sitecontrolled
growth of (GaAs/In0,15Ga0,85As/GaAs) QDs on pre-patterned Si substrate and the direct growth of GaP on Si using migration enhanced
epitaxy (MEE) and MBE growth modes. An efficient ex-situ-buffered HF (BHF) and in-situ surface cleaning sequence based on
atomic hydrogen (AH) cleaning at 500 °C combined with thermal oxide
desorption within a temperature range of 700-900 °C has been
established. The removal of oxide desorption was confirmed by semicircular
streaky reflection high energy electron diffraction (RHEED)
patterns indicating a 2D smooth surface construction prior to the
MBE growth.
The evolution of size, density and shape of the QDs are ex-situ characterized
by atomic-force microscopy (AFM) and transmission electron
microscopy (TEM). The InAs QDs density is strongly increased
from 108 to 1011 cm-2 at V/III ratios in the range of 15-35 (beam
equivalent pressure values). InAs QD formations are not observed
at temperatures of 500 °C and above. Growth experiments on (111)
substrates show orientation dependent QD formation behaviour. A significant shape and size transition with elongated InAs quantum
dots and dashes has been observed on (111) orientation and at higher
Indium-growth rate of 0.3 ML/s. The 2D strain mapping derived
from high-resolution TEM of InAs QDs embedded in silicon matrix
confirmed semi-coherent and fully relaxed QDs embedded in defectfree
silicon matrix. The strain relaxation is released by dislocation
loops exclusively localized along the InAs/Si interfaces and partial
dislocations with stacking faults inside the InAs clusters.
The site controlled growth of GaAs/In0,15Ga0,85As/GaAs nanostructures
has been demonstrated for the first time with 1 μm spacing and
very low nominal deposition thicknesses, directly on pre-patterned Si
without the use of SiO2 mask.
Thin planar GaP layer was successfully grown through migration enhanced
epitaxy (MEE) to initiate a planar GaP wetting layer at the
polar/non-polar interface, which work as a virtual GaP substrate, for
the GaP-MBE subsequently growth on the GaP-MEE layer with total
thickness of 50 nm. The best root mean square (RMS) roughness
value was as good as 1.3 nm. However, these results are highly encouraging
for the realization of III-V optical devices on silicon for
potential applications.