Segregation phenomena and conductivity limits of doped indium oxide thin films

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This project will develop an improved understanding of the limits of electrical conductivity of polycrystalline donor-doped In2O3 thin films. It will be evaluated whether films with higher conduc-tivities than those obtained with present technologies can be realized. Suppressing oxygen incor-poration and avoiding defect segregation at lower processing temperatures are the guiding principles for this goal. We will use magnetron sputtering of differently doped and pre-treated In2O3 targets and co-sputtering to deliberately reduce the oxygen content in the films. Low-temperature deposition with seed layers to enhance crystallization will be employed to suppress equilibration of defect concentrations, which involves surface oxygen exchange and diffusion and dopant diffusion induced segregation. Segregation will be quantified using in-situ X-ray photoelectron spectroscopy, which will also be used to determine the Fermi energy position and the chemical states of indium and the dopants. Thermodynamic and kinetic defect properties are investigated in-operando by high-temperature conductivity and Hall-effect relaxation and annealing measurements in different atmospheres and by Hall-effect measurements with electrochemical polarisation of the samples. Numerical solutions of the time dependent diffusion equation will be performed to describe the corresponding experimental observations. Segregation to grain boundaries will furthermore be validated by determination of grain boundary potential barrier heights using temperature-dependent analysis of the carrier mobility. The measurements shall also clarify why Sn-doped films do not exhibit as high carrier mobilities as films doped with other dopants (for example Zr, Ti, Mo, Ce) for certain carrier concentrations and whether processing routes can be identified by which this limitation can be overcome.