| EXAFS Analysis of Cu2ZnSnS4–like Films and ZnS/Cu2S Multi-Layer Films Prepared Using CVD, ALD | |
| Abstract ID | 14 |
| Presenter | Leila Jewell |
| Presentation Type | Poster |
| Full Author List | Andrew Short, Frank Bridges, Sue A. Carter, Glenn Alers |
| Affiliations | UC Santa Cruz |
| Category | |
| Abstract | We present local structure studies of ZnS/Cu2S and Cu2ZnSnS4 composite films, using extended x-ray absorption fine structure (EXAFS) technique. These films were prepared using atomic layer deposition (ALD) and chemical vapor deposition (CVD), techniques that in principle can deposit conformal films layer by layer and hence are important tools for developing mesoscopic structures. Previous work has shown that individual thin films of ZnS and Cu2S resemble bulk structure. Yet multi-layer films of ZnS/Cu2S prepared using the same parameters as for the individual films do not produce the expected multi-layer film when the individual film layers are roughly 2 nm thick. The films are predominantly either ZnS or Cu2S, with the other material being highly disordered.
To further explore these results, new multi-layer films were formed with a base (~20nm) of ZnS or Cu2S, and thin multi-layers on top. Additional multi-layer films were formed with thicker individual layers (~20nm). The EXAFS data indicate that Zn is entering the multi-layer films in a highly-disordered state, possibly only doping a primarily CuxS film, which is also indicated by the Cu/Zn ratio of these films. In some cases, ZnS oxidation occurs, after the deposition based on the lack of CuO present, which suggests the oxidized ZnS is primarily on the surface where it is unprotected. The results demonstrate that the structure of films with the thinnest layers is dominated by CuxS, whereas in the thicker films the structure is determined by whichever material is first deposited. This can be attributed to the crystal structure mismatch of ZnS and CuxS. To stabilize the structure, Sn was added to attempt to form the well-defined Cu2ZnSnS4 (CZTS) compound. The fluorescence peaks show the material is far from stoichiometric CZTS, with significantly more Zn than Cu in most films and a low Sn signal. Future work will fine-tune the stoichiometry by varying the deposition amounts of each metal. Solar cell applications will be noted. |
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| Funding Acknowledgement | |