Electrical and surface properties of Ge-doped In
2
O
3
thin films
Karoline L. Hoyer, Andreas H. Hubmann, Binxiang Huang, Andreas Klein
Technische Universität Darmstadt, Institute of Materials Science,
Jovanka-Bontschits-Str. 2, 64287 Darmstadt, Germany
Amongst the different dopants studied for In
2
O
3
thin films, Sn is still the one which results in the
highest electrical conductivity. With other dopants such as H, Zr or Ti significantly higher carrier
mobilities are obtained but the maximum carrier concentrations with these dopants are about one
order of magnitude lower than those possible with Sn doping. This is supposedly related to their lower
solubility. The solubility of Sn is, however, also limited. Particularly under reducing atmosphere, Sn
segregates to the surface and to grain boundaries. The latter leads to an enhanced grain boundary
scattering which reduces carrier mobility. Solubility is therefore probably the most critical issue in
obtaining high carrier concentrations. As an alternative dopants we have prepared Ge-doped In
2
O
3
thin films by magnetron sputtering from ceramic targets with different dopant concentrations.
Substrate temperature and oxygen pressure during deposition were varied systematically. The films
are characterised using in-situ photoelectron spectroscopy, Hall-effect and optical transmission as
well as X-ray diffraction. Electrical and optical properties are comparable to those obtained with Sn-
doped films. All films exhibit an enhanced Ge concentration at the surface, which is, in contrast to
ITO, more pronounced under oxidising atmospheres.
PS2 13
-207-
