Atomic Layer Deposition of Conducting CuS Thin Films from Elemental Sulfur

A facile, yet precisely controlled and efficient atomic layer deposition (ALD) process is reported for high-quality copper(II) sulfide thin films based on elemental solid sulfur as the source for sulfur; Cu(acac)₂ (acac: acetylacetonate) is used as the copper precursor. In the deposition temperature range as low as 140-160 °C, the process proceeds in an essentially ideal ALD manner and yields single-phase CuS thin films with appreciably high growth rate of ≈4 Å per cycle. When the deposition temperature is increased above 160 °C the growth rate considerably increases and flake-like nanostructures evolve. All the as-deposited films are crystalline, highly conducting, and specularly reflecting. Seebeck coefficient measurements confirm the p-type conducting nature of the films. The direct optical bandgap as determined from UV-vis spectroscopic measurements varies in the range of 2.40-2.54 eV, depending on the deposition temperature.