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Ge‐doped In2O3 thin films prepared by magnetron sputtering are studied using photoelectron spectroscopy and Hall effect measurements. Carrier conductivities of up to 8.35thinmathspace×thinmathspace103cm−1 and carrier mobilities of up to 57thinmathspacecm2thinmathspaceV−1s−1 are observed. The surface Ge concentration is enhanced by a factor of 2–3 compared to the concentration in the interior of the films. The surface Ge concentration increases with more oxidizing deposition conditions, in opposite to what has been reported for Sn‐doped In2O3. Ge‐doped In2O3 films exhibit higher work functions as compared to Sn‐doped films, in particular at oxidizing conditions. This is attributed to the formation of a GeO2 surface phase. While segregation of Sn reduces the carrier mobility due to grain boundary scattering, Ge segregation does not show such an effect. The differences are attributed to the different oxidation states of the segregated dopants, in agreement with the observed dependence of segregation on oxygen activity.

The modification of the work function of Sn-doped In 2 O 3 (ITO) by vacuum adsorption of 4-(Dimethylamino)benzoic acid (4-DMABA) has been studied using in situ photoelectron spectroscopy. Adsorption of 4-DMABA is self-limited with an approximate thickness of a single monolayer. The lowest work function obtained is 2.82 ± 0.1 eV, enabling electron injection into many organic materials. In order to identify a potential influence of the ITO substrate surface on the final work function, different ITO surface orientations and treatments have been applied. Despite the expected differences in substrate work function and chemical bonding of 4-DMABA to the substrate, no influence of substrate surface orientation is identified. The resulting work function of ITO/4-DMABA substrates can be described by a constant ionization potential of the adsorbed 4-DMABA of 5.00 ± 0.08 eV, a constant band alignment between ITO and 4-DMABA and a varying Fermi energy in the ITO substrate. This corresponds to the behaviour of a conventional semiconductor heterostructure and deviates from the vacuum level alignment of interfaces between organic compounds. The difference is likely related to a stronger chemical bonding at the ITO/4-DMABA interface compared to the van der Waals bonding at interfaces between organic compounds.

For the application as transparent conductive material, In2O3 is mostly doped with 10 wt. % SnO2. At such high dopant concentrations the Sn‐donors, which are mobile at temperatures of 300°C or higher, can segregate to grain boundaries and to the surfaces of the films. The segregation preferentially occurs under reducing conditions, i.e. for the most conductive samples. As a consequence, carrier mobility is lowered by grain boundary scattering. Whether the segregation to the surface affects the work function could not be identified for ITO. This is different in the case of Ge‐doped In2O3. The Ge‐concentration at the surface attains values of up to 25 cation% (GGI) depending on substrate temperature and atmosphere during film deposition. This corresponds to an increase of up to a factor of 3 compared to the bulk concentration. The increased surface Ge concentration is clearly accompanied by an increase of the ionization potential from 7.4 to 8 eV, as shown in the inset of the figure. As the segregation of Ge preferentially occurs under oxidizing conditions, highly conductive films exhibit higher carrier concentrations when doped with Ge compared to Sn‐doped films. For further details refer to the article by Hoyer et al. (No. http://doi.wiley.com/10.1002/pssa.201600486).