| AVS 60th International Symposium and Exhibition | |
| Energy Frontiers Focus Topic | Monday Sessions |
| Session EN+PS+TF-MoM |
| Session: | Thin Film, Organic, and Chalcogenide Solar Cells |
| Presenter: | P. Peña Martin, University of Illinois at Urbana Champaign |
| Authors: | P. Peña Martin, University of Illinois at Urbana Champaign A. Rockett, University of Illinois at Urbana Champaign |
| Correspondent: | Click to Email |
The chalcopyrite system has contributed the top performing absorber layer for thin film photovoltaic devices, Cu(In,Ga)Se2, but the surface properties of these compounds are not well understood. While CuInSe2 (CIS) has proven difficult to obtain atomically resolved surface images, the AgInSe2 (AIS) surface has been recently observed. Study of the surface structure, growth mechanics and defects of AIS can provide important details of its behavior, as well as yielding insight into other chalcopyrites, like CIS, by comparison of the results. This work presents the results of growing epitaxial AIS films and studying their surface morphology to help understand its growth behavior and to transfer this knowledge to help understand the growth of chalcopyrites in general.
Thin films of AIS were grown by hybrid sputtering and evaporation technique on (110), (110), (111), and (-1-1-1) GaAs substrates. Film thicknesses were around 500 nm, and the substrate temperature was varied from 500-700°C. Their microstructures were characterized by a variety of techniques including scanning electron (SEM), scanning tunneling (STM), and atomic force (AFM) microscopies, as well as x-ray diffraction (XRD). SEM shows that the films all exhibit facets or features that are aligned across the sample, indicating that the films are epitaxial, confirmed by x-ray diffraction.
AIS was found to show a similar preference as does CIS for polar facets. The films grown on GaAs (111) and (-1-1-1) are very smooth with individual atomic steps resolvable, while growth on GaAs (110) results in films that spontaneously facet to two polar faces with roughnesses that differ dramatically. AFM line profiles indicate an angle of ~68° between the faces, as expected for the angle between polar (112) planes. One side of the facets is stepped, with triangular features pointed toward the “peak” of the facet. The other side shows fewer features, with occasional triangular terraces pointed toward the “valley” instead. This is consistent with a chemical difference between these two surfaces. The films grown on (100) GaAs are highly featured, with rectangular pits that are likely (111) terminated. The features on films grown on both (100) and (110) substrates both show smaller size than films grown on CIS, even with a higher homologous temperature for AIS.