Optimization of the post-deposition annealing process of high-mobility In2O3:H for photovoltaic applications

High-mobility hydrogen-doped indium oxide In2O3:H (IOH) were deposited by magnetron sputtering (radio frequency 13.56 MHz) from an In2O3 target in Ar/O2/H2O gas mixtures onto unheated substrates. The as-deposited films were amorphous as shown by X-ray measurements and were crystallized in a post-annealing step in vacuum and air at 180 °C for 15 min. The optical, electrical, and morphological properties as well as the crystallization behavior of these transparent conductive oxides films were investigated in detail. A dependence of the annealing behavior in air on the total pressure during deposition could be shown. High carrier mobilities > 100 cm2/Vs allow for very low optical absorption and a low resistivity around 350 μΩcm. Amorphous IOH films were crystallized by short-term flash lamp annealing (FLA) in argon atmosphere for around 2.7 ms. Spatial temperature distributions in a typical layer stack (crystalline silicon, amorphous silicon, silicon oxide, and IOH film) were calculated within milliseconds after the FLA-treatment. Electron backscattering diffraction measurements of IOH films crystallized by FLA reveal a polycrystalline microstructure with an average lateral crystallite size of 333 nm. The crystallization process of these IOH films was studied by XRD and Hall measurements.