In Situ Fluorine Doping of FZO Films by Atomic Layer Deposition

In optoelectronic devices, fluorine-doped semiconductors have been used widely. Atomic layer deposition (ALD) is one of the main processes integrated into semiconductor manufacturing and a perfect candidate to obtain conformally covered films for complex geometries at low temperatures on a budget. Due to the lack of a proper fluorine source, fluorine doping with ALD has been a challenge. In this study, fluorine-doped ZnO (FZO) thin films by ALD were successfully achieved, demonstrating the efficiency and practicality of a new homemade precursor mixture: ammonium fluoride/water (NH₄F/DI) solution. The fluorine incorporation mechanism was investigated and discussed in detail with respect to growth conditions. The effects of ALD growth temperature (160-200 °C), canister temperature (RT, 40 °C, and 50 °C), and concentration of NH₄F/DI water mixture (20-40%) on fluorine doping, crystallinity, atomic-scale interactions, and electrical and optical properties were investigated. For the fluorine doping conditions identified as 180 °C growth temperature with a 30% NH₄F/DI water mixture and a 40 °C canister temperature, a fluorine incorporation of 2.62 at. % F was achieved.