Atomic Layer Deposition of Conducting CuS Thin Films from Elemental Sulfur

Abstract

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...

Effect of RF Power on the Properties of Sputtered-CuS Thin Films for Photovoltaic Applications

“…CuS thin films are generally grown by methods like spray pyrolysis [8], the hydrothermal method [9], chemical-vapor deposition [10], atomic-layer deposition [11], and sputtering [12]. Among these, radio-frequency (RF) magnetron sputtering, which is one of the physical vapor-deposition methods, employs simple equipment and can form a strong adhesive force between the as-sputtered thin films and the substrate.…”

Atomic and Molecular Layer Deposition of Alkali Metal Based Thin Films

“…Prototypical ALD processes include those for binary metal oxides (e.g., Al 2 O 3 , HfO 2 , TiO 2 , ZnO) , and sulfides (e.g., ZnS), but ternary and even quaternary processes are possible as well, though more challenging to optimize. − Organometallic compounds such as trimethylaluminum (TMA) and diethylzinc (DEZ) or metal halides such as TiCl 4 or HfCl 4 are usually used as the metal precursors, as they have much lower sublimation/evaporation temperatures than, for example, elemental metals, thus allowing for the reactor to be operated at a reasonably low temperature. The second precursor is then typically the source of oxygen (e.g., H 2 O, O 3 ), sulfur (e.g., H 2 S, S), , or nitrogen (e.g., NH 3 ) …”

Activated Carbon and Metal Chalcogenide in Applied Materials Research

“…These sample are p-type films, band gap values in the ranges of 2.4 to 2.54 eV. Higher growth arte and flake like morphology could be observed when the temperature was increased above 160°C [52]. H 2 S was used to provide sulphur ion [53] during the deposition process at 130 to 200°C.…”