Biennial Report 2016/2017

Selected Results
Novel Setup for Investigation of Ion Energy and Ion Mass Selective
Hyperthermal Ion-Beam Assisted Deposition Processes
J.W. Gerlach, P. Schumacher, M. Mensing, B. Rauschenbach
in collaboration with
S. Rauschenbach, MPI-FKF Stuttgart / University of Oxford, UK, I. Cermak, CGC Instruments, Chemnitz
Ion-beam assisted deposition (IBAD) is a highly
effective hybrid physical thin film deposition
technique which on the one hand offers the
opportunity to investigate fundamental processes
involved in ion-assisted film growth and on the
other hand provides manifold possibilities to
intentionally modify the properties of the prepared
thin films [1]. The technique is characterized by
simultaneous irradiation of the growing thin film
with energetic ions during deposition with the aim
to significantly influence the growth processes
themselves. In contrast to other physical
deposition methods like e.g. magnetron sputtering
or pulsed laser deposition, IBAD is mainly defined
by the separability of the involved material fluxes,
which are directed towards the sample, as well as
by the possibility to adjust the parameters vapor
flux and ion flux highly accurate, the latter
generated in form of a broad ion beam. As for
nitrogen ion beams however, nitrogen plasma
based ion-beam sources counteract the demand
to choose the ion-beam parameters as freely as
possible, because (i) the resulting ion beam
consists of a blend of both molecular (N 2 + ) and
atomic nitrogen ions (N + ) and (ii) both species can
possess differing kinetic energy distributions.
Particularly in the case of hyperthermal ion
energies ranging from several 10 eV to a few
100 eV this creates great difficulties to input the
ion energy into the growing film surface in a welldefined
and well-controlled way. Therefore, in
Figure 2: Demonstration of ion-beam mass separation by the
quadrupole setup using a nitrogen plasma-based source [2].
order to create a hyperthermal, broad nitrogen ion
beam with selectable ion mass and variable ion
energy, in recent years a compact, custom
prototype quadrupole setup (Fig. 1) was
developed, built, implemented into the system for
ion-beam assisted molecular-beam epitaxy (IBA-
MBE) at the IOM and characterized (for details
see Ref. [2]). For this purpose, a constricted glowdischarge
plasma beam source or instead a
Kaufman-type ion-beam source was combined
with the novel setup consisting of a quadrupole
mass filter (Fig. 2), equipped with entry and exit
ion optics, ion-beam deflection, as well as ionbeam
current monitoring facilities.
As a model system for hyperthermal ion-beam
assisted growth with energy and mass selected
ions (EMS-IBAD), thin films of gallium nitride
(GaN) - well known as base material for
optoelectronics and high power electronics
devices - were deposited epitaxially on singlecrystalline
substrates at elevated temperatures.
The influences of ion mass and ion energy on
growth mode, topography, crystalline quality,
defect structure and luminescence properties of
these GaN thin films have been investigated.
Figure 1: Design of the quadrupole mass filter setup for the
creation of an energy and mass selective hyperthermal
nitrogen ion beam [2].
Literature
[1] B. Rauschenbach, A. Lotnyk, L. Neumann, D. Poppitz,
J.W. Gerlach, Materials 10 (2017) 690.
[2] J.W. Gerlach, P. Schumacher, M. Mensing, S.
Rauschenbach, I. Cermak, B. Rauschenbach, Rev. Sci.
Instrum. 88 (2017) 063306.
45