Copper sulfide thin films have been fabricated by various deposition techniques, such as chemical vapor deposition, [15] sputtering, spray pyrolysis, [16,17] chemical bath deposition, [18,19] and electrochemical methods. [20][21][22] However, in most cases the required control over the film stoichiometry and phase composition is poorly achieved due to the coexistence of several stable and metastable copper sulfide phases. [23] Moreover, fabrication of continuous copper sulfide coatings with a well-controlled morphology on highaspect-ratio nanostructures has remained a challenge. It is here in particular where the atomic layer deposition (ALD) technique could provide us with clear advantages over the other thin-film technologies for the deposition of high-quality copper sulfide thin films for various advanced applications including the photovoltaics. [17,24,25] Atomic layer deposition is based on sequential and self-limiting gas-surface reactions and is known to yield exceptionally homogeneous coatings in atomic-scale precision independent of the substrate geometry.The vast majority of the metal sulfide ALD processes is based on metal-organic precursors together with hydrogen sulfide H 2 S as the source of sulfur; [26] the same applies to the reported copper sulfide ALD processes as well (see Table 1). The main merit of H 2 S is that it is highly reactive toward common metal precursors. However, H 2 S is a flammable, corrosive, and highly toxic gas, and its incorporation in the ALD technology presents several serious technical challenges. The special precautions required for the safe use of H 2 S may even be one of the reasons why only 16 metal sulfide ALD processes have been so far reported during the half a century long ALD history. [26] Another drawback of the H 2 S-based ALD processes is the slowness of these processes, see, e.g., the growth rate values given in Table 1 for the copper sulfide processes. Moreover, majority of the reported copper sulfide processes yields Cu(I) sulfide as the main phase; hence, there is a clear interest in a new robust and efficient ALD process for high-quality Cu(II) sulfide thin films. [27] Despite the fact that some of the early ALD processes employed elemental sulfur instead of H 2 S as the sulfur source, [35] to the best of our knowledge no sulfur-based ALD processes have been reported for copper sulfide thin films. Here, we present a simple and efficient low-temperature ALD process for the deposition of high-quality p-type conducting CuS thin films from copper acetyl acetonate and elemental sulfur precursors, as a highly viable solution to the challenges discussed above.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 C...
