Improved electrical properties of pulsed DC magnetron sputtered hydrogen doped indium oxide after annealing in air

Its high electron mobility makes hydrogen doped indium oxide (IOH) a promising transparent conductive oxide for photovoltaic and other applications. We report on a deposition process for IOH that is attractive for industrial application, using large area pulsed direct current (DC) magnetron sputtering and annealing in air. Structural, optical and electrical properties as well as stability of films annealed in air were assessed and compared to vacuum annealed films. Critical factors were found to be water and oxygen partial pressures during the sputter process, which, when chosen inappropriately, can cause a low density film structure, enhancing diffusion of atmospheric species into the indium oxide layer during crystallization in air. This leads to a lower charge carrier density of air annealed films compared to vacuum annealed films. We introduce a bi-layer stack to reduce diffusion processes during air annealing and thus improve the charge carrier density without adversely affecting the electron mobility or optical absorption.