# Recent Advances in the Growth and Characterizations of SILAR-Deposited Thin Films
## 2 Metal Sulfide Thin Films
### Copper sulfide Films  
The copper sulfide (CuS) films were deposited onto various substrates (glass and Si(111) wafer) by using a thiourea and copper (II) sulfate (CuSO\({}_{4}\)) solution [46]. Highly polycrystalline films were produced by using a Na\({}_{2}\)S and CuSO\({}_{4}\) solution. The obtained films showed uniform morphology with the covellite phase and could be used for optoelectronic device applications [47]. The cupric sulfate (CuSO\({}_{4}\)) and sodium thiosulfate (Na\({}_{2}\)S\({}_{2}\)O\({}_{3}\)) were employed to form CuS films at room temperature. A significant change in the surface morphology of the films could be observed at 100 cycles (irregular microspheres), 150 cycles (bigger in size), and 200 cycles (flower-like agglomerated grains). Overall results indicated a high absorbance value in the visible range, excellent optical features, and a direct band gap value (1.95 eV to 1.98 eV). The growth of CuS films under normal pressure was studied. The researchers pointed out that the films were rough and the growth rate was proportional to the copper concentration [48]. The influences of the molar concentration on the films were investigated. The band gap dropped (2.26 to 1.86 eV) when increasing the molar concentration (0.05 to 0.25 M). The average transmittance observed was more than 70% of the UV-visible-NIR regions in all films, indicating excellent materials for the optical coatings [49]. The Cu\({}_{2}\)S films were produced [50] by using different complex agents, such as a hexamethylenetetramine ((CH\({}_{2}\))\({}_{6}\)N\({}_{4}\)) and ammonia solution (rinse time was 30 s, immersion time was 20 s, deposition cycles = 100 cycles). The copper sulfate provided cationic ions reacted with the ammonia solution to prepare Cu(OH)\({}_{2}\) (solution became turbid) as indicated in equation 10. Then, the complex ion [Cu(NH\({}_{3}\))\({}_{4}^{2+}\)] was produced (solution became clear) by adding the excess ammonia solution as highlighted in \begin{table}
\begin{tabular}{c c c} \hline \multicolumn{3}{c}{**Similarity Results:**} \\ \hline Crystallinity & Better crystallinity could be observed due to the higher surface mobility of the impinging atoms. & Poor crystallinity. \\ \hline Crystallite size & Larger crystallite size could be observed due to the higher adatom mobility; 19, 29, and 32 nm were found when the film thickness was 330, 440, and 550 nm, respectively. & Smaller crystallite size could be observed; 4.1, 6.2, and 12.4 nm were found when the film thickness was 330, 440, and 550 nm, respectively. \\ \hline Absorption value & Low absorption in the ultraviolet region. & High absorption in the ultraviolet region due to the granular structure. \\ \hline Absorption coefficient & Low absorption coefficient value. & Can absorb UV light more efficiently and produce high optoelectronic conversion efficiency because of the high absorption coefficient value. \\ \hline Carrier mobility & A higher carrier mobility could be observed (23 to 37.5 cm\({}^{2}\)V\({}^{-1}\)S\({}^{-1}\)) when the film thickness was 330–550 nm. & A low carrier mobility could be observed (6.5 to 18.5 cm\({}^{2}\)V\({}^{-1}\)S\({}^{-1}\)) when the film thickness was 330–550 nm. \\ \hline Carrier concentration & A higher carrier concentration could be observed (26 \(\times\) 10\({}^{14}\) to 73 \(\times\) 10\({}^{14}\) cm\({}^{-3}\)) when the film thickness was 330–550 nm. \\ \hline \multicolumn{3}{c}{Low resistivity could be observed} & High resistivity could be observed (4.3 to 10.8 ohm-cm) when the film thickness was 330–550 nm. \\ \hline Resistivity & Low resistivity could be observed (4.3 to 10.8 ohm-cm) when the film thickness was 330–550 nm. \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._Equation (11). Here, the most stable coordination number should be 4. Based on the experiment, a similar type of reaction occurred by using hexamethylenettermine (Equation (12)).