Atomic layer deposition of Cu₂O using copper acetylacetonate

Cu2O is an important p-type semiconductor material with applications in thin-film transistors, photovoltaics, and water splitting. For such applications, pinhole-free and uniform thin films are desirable, thus making atomic layer deposition (ALD) the ideal fabrication technique. However, existing ALD Cu precursors suffer from various problems, including limited thermal stability, fluorination, or narrow temperature windows. Additionally, some processes result in CuO films instead of Cu2O. Therefore, it is important to explore alternative precursors and processes for ALD of Cu2O thin films. In this work, we report the successful deposition of Cu2O using copper acetylacetonate as a precursor and a combination of water and oxygen as reactants at 200 °C. Saturation of the deposition rate with precursor and reactant dose time was observed, indicating self-limiting behavior, with a saturated growth-per-cycle of 0.07 Å. The Cu2O film was polycrystalline and uniform (RMS roughness ∼2 nm), with a direct forbidden bandgap of 2.07 eV and a direct allowed bandgap of 2.60 eV.