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

Experimental Growth and Characterization Techniques
from a two-dimensional net of atoms on the surface, the reciprocal lattice comprises
a set of rods perpendicular to the surface in real space. If the Ewald sphere
is so large compared to the separation of the reciprocal lattice rods that it will
intersect several rods, then it will excite several Bragg reections for any given
geometry. Therefore, the diraction pattern therefore comprises a set of streaks
indicating 2D crystalline surface as shown in Fig. 4.2(b).
The growth rate may be determined from RHEED intensity oscillations, for
which the period corresponds to one monolayer of growth. The surface roughness,
and therefore the growth mode, may be discerned from the nature of the RHEED
pattern. As noted previously, a streaky pattern is an indication of an atomically
at surface. In the case of a rough surface, the electron beam will penetrate
islands or other structures on the surface, giving rise to diraction from a threedimensional
lattice. Therefore, the RHEED pattern becomes spotty in this case
as shown in Fig. 4.2(a). The very macroscopic nature of this technique, which
lessens its impact in determining exact microscopic structure, is exactly what
makes it such a powerful and crucial in-situ tool for the epitaxial crystals grower
in determining epitaxial layer quality in real-time during growth
4.2.2 Electron Beam Evaporator system for Silicon Homoepitaxy
Another important modication to the Varian Gen II MBE system was the installation
of a new electron beam evaporation (EBE) cell from Carrera systems
and MBE components for high quality pure silicon homoepitaxial growth. This
system consist mainly by three main parts. A high energy electron gun with
input voltage up to 10 keV and lament current of 100 mA, and crucible at the
middle position dedicated for target loading as shown in Fig. 4.4(b), an electron
evaporation controller to control the area and the position of the exposed area
of the silicon target, and a deposition sensor equipped with a quartz crystal to
measure the growth rate and the thickness of the deposited layer as shown in
Fig. 4.3.
The process begins under UHV condition of 10 −9 T orr. A tungsten lament
inside the electron beam gun is heated. The gun assembly is located outside the
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