Influence of dopant segregation on the work function and electrical properties of Ge-doped in comparison to Sn-doped In₂ O₃ thin films (Phys. Status Solidi A 2∕2017)

Abstract

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).