Semiconducting Amorphous Fe-Si Films And The Interpretation Using The Cluster Model

The semiconducting amorphous Fe-Si films have the performance approximating to crystalline phase ?-FeSi2 at room temperature. It is a low-cost, high-efficiency photovoltaic material. The semiconducting amorphous Fe-Si films can not only avoid the limitation of composition and preparation of ?-FeSi2, but also avoid the problem of film-substrate interface mismatching in silicon-based technology applications. It can be synthesized by using more economical techniques and compatible with silicon IC technologies. In additions, it has a potential application as compared with amorphous silicon. Furthermore, amorphous Fe-Si films consider to be a promising semiconductor material in amorphous materials, which is expected to be applied to the various devices applications such as:silicon-based optoelectronic devices, solar cells and near infrared detector.The short-range ordering in the amorphous phase determines the final performance. But there are no systematic studies on the composition range of amorphous Fe100-xSix films corresponding to semiconducting performance and local structure. This is essential for the preparation and rational use of amorphous Fe100-xSix films. Moreover, with the adding of M elements in the Fe-Si binary system, it can not only improve the amorphous formation ability, but also expand the scope of its ingredients. Therefore, it increases the flexibility of applications of amorphous Fe100-xSix thin films.In the present paper, Fe100-xSix (x=30.3-100 at.%) and Fe-Si-M (M= Mn or C) ternary amorphous films were prepared on single crystal Si (100) and Al2O3 (0001) substrates by magnetron sputtering RF magnetron co-sputtering, and were analyzed for composition, microstructure, optical band gap, crystalline phase, resistivity and stability. The relationship between the composition of amorphous Fe-Si films and the local structure was determined from the perspectives of experiment and theory, and the local structure of amorphous Fe100-xSix was analyzed by amorphous structure model.Our recent study showed that variation of composition result in different change in performance as follows:30.3?x?50, the non-semiconducting performance zone; 50<x<87.5, the semiconducting performance zone with a direct band gap; 87.5?x?100, the semiconducting performance region with an indirect band gap. Furthermore, [cluster] (glue atom) 1 or 3 amorphous structural model was adopted to study the local structure of films. Then, three short-range ordered cluster structures including [Fe-Si7Fe6], [Fe-Si8Fe2] and [Si-Si4], which were determined by ?-FeSi, ?-FeSi2 and Si phases, were found in the entire composition range. They can just divide the composition into three main zones by alone or superimposed, which coincides with above analysis. The optical absorption coefficient of films decreased, and optical band gap were relatively stable (-0.92 eV) after annealing, almost invariant with the annealing time and composition of thin films.The doping of M (Mn or C) has no significant effects on the optical band gap and electrical resistivity. However, the doping of C can improve the stability of amorphous films significantly.These studies are of practical significance to extend the applications of amorphous Fe100-xSix film with semiconducting performance.