High-Mobility Hydrogenated Indium Oxide Without Introducing Water During Sputtering

The key role of water to obtain high-mobility IO:H (hydrogenated indium oxide) layers has been well documented, but introducing the required tiny amount of water is technologically challenging. We first use simulations to evidence the key role of high mobility for the transparent conductive oxide for high-efficiency crystalline silicon solar cells. Then, we investigate an approach to fabricate high-mobility IO:H that circumvent the introduction of water vapor, relying on water vapor from ambient air. A sputtering tool equipped with a residual gas analyzer allows partial pressure monitoring of hydrogen and water in the system, and to link the gas composition to the properties of the deposited films. To vary the residual water pressure, we varied the pumping time after opening the chamber and before starting the deposition to reach different base pressures (1. 10^-5 mbar to 3. 10^-7 mbar), which are mostly composed of residual water. An optimum base pressure around 3. 10^-6 mbar - and not lower pressures - was found to yield the highest mobility values after annealing. An alternative approach by introducing a small flow of hydrogen together with argon and oxygen is also shown to provide promising results.