Atomic layer deposition of copper sulfide thin films

Abstract Atomic Layer Deposition (ALD) of copper sulfide (Cu x S) thin films from Cu(acac) 2 (acac = acetylacetonate = 2,4-pentanedionate) and H 2 S as Cu and S precursors is reported. Typical self-saturated reactions (“ALD window”) are obtained in the temperature range T dep = 130–200 °C for an average growth per cycle (GR) = 0.25 A/cycle. The morphology, crystallographic structure, chemical composition, electrical properties and optical band gap of thin films were investigated using scanning electronic microscopy (SEM), X-ray diffraction under Grazing Incidence conditions (GI-XRD), X-ray reflectivity (XRR), energy dispersive spectrometry (EDS), Hall effect measurements, and UV–vis spectroscopy. The obtained copper sulfide films are heavily p-doped (charge carrier concentration ~ 10 21 –10 22 cm − 3 ) with optical band gaps in the range of 2.2–2.5 eV for direct and 1.6–1.8 eV for indirect band gaps. Depending on the number of ALD cycles, multiphase compounds (made of digenite Cu 1.8 S, chalcocite Cu 2 S, djurleite Cu 31 S 16 and covellite CuS) or single-phase digenite Cu 1.8 S films are obtained via a growth mechanism that involves in-situ copper reduction and loss of sulfur by evaporation.