Transition from amorphous to crystalline beta phase in co-sputtered FeSi2 films as a function of temperature

Abstract

A study of the stability of amorphous FeSi 2 films and their transition to a crystalline phase as a function of deposition or annealing temperature is presented. Stoichiometric FeSi 2 films, 300-400 nm thick, were deposited on ͑100͒ Si substrates by co-sputtering of Fe and Si. It was found that the films grow in an amorphous form for the substrate temperature ranging from room temperature to 200°C, while from 300-700°C, they grow in form of a crystalline ␤-FeSi 2 phase. In a postdeposition 30 min heat treatments, the layers retain the amorphous structure up to 400°C, transforming to the crystalline ␤ phase at 500-700°C. The results are discussed in the frame of the existing models, and compared to those found in the literature. It is shown that in as-deposited films, the growth is controlled by surface diffusion, the crystalline layers growing in a columnar structure strongly correlated to the Si substrate. Postdeposition treatments induce a random crystallization controlled by bulk diffusion, the resulting structure not being influenced by the substrate. The results of this work contribute to a better understanding of the processes involved in a transition of amorphous FeSi 2 films to a crystalline phase, and provide a basis to determine the processing parameters in potential applications of this promising semiconducting material.

Theoretical and experimental study of semiconducting iron disilicide and its applications to thin film solar cells

“…This observation is not surprising since typically in a post-deposition annealing the random crystallization process is mainly controlled by bulk diffusion and therefore the substrate has minimal influence on the resulting structure. Our observation on the transition from amorphous to polycrystalline β-phase FeSi 2 agrees with that reported in the literature for the case of cosputtered FeSi 2 films[129].…”

Phase composition evolution of iron silicide nanocrystals in the course of embedding into monocrystalline silicon

“…To reduce internal energy reaction ɛ-FeSi + Si = β-FeSi2 takes place in NCs [19]. This phase transition is observed in small NCs, while in big ones β-FeSi2 is formed only at the NC/substrate interface and blocks silicon diffusion inside the ɛ-FeSi part of the NC [20].…”

“…, 011401 (2017) shape became semispherical (not shown). Taking into account that Si diffusion into the NCs at 750 °C is higher than that at 630 °C [20], one can suggest that this transformation results from reactions β-FeSi2 = α-FeSi2 + ɛ-FeSi and ɛ-FeSi + Si = α-FeSi2 [21], since Si-rich α-FeSi2 phase has lower internal energy than β-FeSi2 and ɛ-FeSi at 750 °C. In large ion beam synthesized β-FeSi2 grains (up to 150 μm), β-FeSi2 to α-FeSi2 phase transition occur at a temperature higher than 950 °C [21,22].…”

Photovoltaic properties of n-Type nanocrystalline-FeSi2/intrinsic-Si/p-Type Si heterojunctions fabricated by facing-targets DC sputtering

“…Nanocrystalline iron disilicide (NC-FeSi 2 ) is a novel semiconducting material exhibiting semiconducting properties close to that of amorphous FeSi 2 [1,2]. NC-FeSi 2 comprises crystallites with diameters ranging from 3 to 5 nm [3].…”