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

5.3 Results and Discussion
25-32 nm (Fig. 5.3(b),(c)) and a signicant enhancement of the homogeneity of
the dot distributions.
5.3.3 InAs Quantum Dots Grown on Silicon Buer Layer
The inuence of the growth parameters on the structural properties (size, density
and shape) of InAs QDs like In-growth rate, V/III ratio, growth temperature and
InAs coverage, were investigated using the following conditions: Ga treatment for
2 min (0.1 ML/s) at 560 ◦ C, thermal desorption at 870 ◦ C for 15 min, 50 nm
Si buer grown at 700 ◦ C, 10 min post growth annealing (PGA) at 800 ◦ C on
n-doped Si (100) substrate have been performed for all the samples before InAs
deposition for additional crystallinity improvement. The growth conditions used
here are: V/III ratio 25, growth temperature at 400 ◦ C, Indium (In) growth rate
= 108 nm/h, 2 MLs InAs coverage and only one growth parameter was changed
(see subsections below).
5.3.3.1 Homoepitaxy of Silicon Buer Layer
After in-situ (thermal desorption at 870 ◦ C for 15 min.) and ex-situ (wet etching
using buered HF) surface treatment of Si substrate, a silicon buer layer
was grown. The electron beam evaporator cell in MBE Gen II was calibrated
using two samples. In order to calculate the real growth rate of the (EBE) cell
at given emission current I emission and voltage V . Two samples with dierent
thicknesses of 50 and 100 nm, respectively were grown according to deposition
controller measurements (quartz crystal sensor). However, at the same time the
preparation time for each sample was recorded. The real thickness of each sample
was measured via prolometer. From thickness measurements, the tooling factor
was extracted using Eq. 5.6.
T ooling factor =
T hickness profilometer(real)
× 100 (5.6)
T hickness deposition controller
This tooling factor value (correction factor) was inserted later in the software
of the deposition controller to read the real deposition rate of the silicon cell. The
growth parameters which were used for the calibration are; I emission = 72 mA, V
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