Does the dopant influence the texture of magnetron sputtered In2O3 thin films?
Andreas H. Hubmann, Mareike V. Frischbier, Hans F. Wardenga, Karoline L. Hoyer,
Andreas Klein
Technische Universität Darmstadt, Institute of Materials Science, Jovanka-Bontschits-
Strasse 2, 64287 Darmstadt, Germany
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Doped In2O3 thin films are commonly prepared in polycrystalline form by various thin film
deposition methods. Due to the dependence of the surface potentials – work function and
ionization potential – on surface orientation, the preparation of films with a well-defined
surface orientation may be advantageous for some applications. In particular, (100) oriented
surfaces might be desirable, as they allow for a considerable variation of surface potentials.
Density functional theory calculations reveal that (111) the oriented surface is the most stable
for most oxygen chemical potentials. In addition to surface energy, other factors such as
strain, ion bombardment, substrate material and crystallinity will also affect the
crystallographic orientation of the films, which determines the surface orientation. The
crystallographic orientation of differently doped In2O3 films, as obtained by X-ray
diffraction, has been monitored over a time period of more than 10 years. We find that
undoped In2O3 films are mostly randomly oriented with either a weak (211) or a weak (100)
texture, while hydrogen doping leads to a pronounced (100) texture. Zr-, Ge- and the widely
used Sn doping result in a preferred (211) orientation in most cases. Only Sn-doped films
deposited at high substrate temperatures (600°C) show a clear (100) orientation, which is not
observed for Zr and Ge doping. ITO films with a strong (100)-orientation can also be
prepared at lower substrate temperature using the recipe for H-doped In2O3. However, (100)
oriented ITO films exhibit much lower carrier mobility, which is assigned to segregation of
the dopant to the grain boundary.
PS1 30
-186-
