Growth of Cu ₂ S thin films by atomic layer deposition using Cu(dmamb) ₂ and H ₂ S

In this study, atomic layer deposition (ALD) of Cu ₂ S was explored using bis(dimethylamino-2-methyl-2-butoxy)copper(II) and 5% H ₂ S combination as Cu and S sources, respectively. The reaction resulted in a high growth rate of ∼0.22–0.24 nm/cycle at 150–200 °C owing to the high reactivity of the Cu precursor. At all investigated temperatures, Cu ₂ S films with Cu oxidation state of +1 were obtained with negligible impurity levels. It was revealed that stoichiometric Cu ₂ S films could be deposited at 120–150 °C, while sulfur deficient films was formed at 200 °C. Cu ₂ S ALD process at low temperatures of 100–120 °C resulted in continuous film formation while the higher deposition temperatures of >150 °C led to island formation. Cu ₂ S films showed p-type electrical characteristic with high hole concentrations of 4 × 10 ¹⁹ –10 ²¹ cm ⁻³ and Hall mobility of 2 cm ² /vs. Lastly, the as-deposited Cu ₂ S films exhibited an optical band gap of 1.2 eV which widened upon prolonged surface oxidation and in addition displayed NIR intra-band absorption.