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

4.2 Molecular Beam Epitaxy Technique
Figure 4.2: (a) 3D sketch shows the directions of the elastically scattered electrons in
real space. These scattered electron beams hit a uorescent RHEED screen in certain
RHEED spots, lying on so-called Laue circles which are numbered starting from zero.
(b) Streaks RHEED pattern indicates a 2D surface for Ewald sphere larger than the
separation of the reciprocal lattice rods [33, 29].
MBE system used for the work presented here has a RHEED system consisting of
a high energy electron gun capable of 35 kV beam energy and a phosphor coated
screen with recording camera on the opposite side of the chamber to record the
RHEED patterns, as shown in Fig. 4.1.
In a typical RHEED experiment, a high energy beam of electrons is incident on
the sample surface at a shallow angle of 1 to 2 ◦ (reection condition). Diraction
of the electrons is governed by the Bragg law, as with x-ray diraction. However,
there are two important dierences between RHEED and the x-ray case.
First, the electrons do not penetrate signicantly into the sample, so diraction
is essentially from the two-dimensional lattice on the surface. Second, for the
high energy electrons used in RHEED, the Ewald sphere is large in diameter,
so many reections are excited at once. RHEED is a surface sensitive technique
that provides a real time prole of the atomic surface periodicity during MBE
growth. The reection from the substrate is directed toward a phosphor screen,
displaying a pseudo-1D diraction pattern during growth or prior to the growth
in preparation stage [33].
The intensity of the reected RHEED spots/streaks is sensitive to the atomic
arrangement of atoms on the substrate surface. Because the diraction occurs
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