Influence of dopant segregation on the work function and electrical properties of Ge-doped in comparison to Sn-doped In2O3 thin films

Ge-doped In2O3 thin films prepared by magnetron sputtering are studied using photoelectron spectroscopy and Hall effect measurements. Carrier conductivities of up to 8.35 Chi 10(3) S cm(-1) and carrier mobilities of up to 57 cm(2) V(-1)s(-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.