Fabrication of BaSi2 thin films capped with amorphous Si using a single evaporation source

The capping of a BaSi2 film with amorphous Si (a-Si) is a key technology for the solar cell applications of BaSi2. In this study, we have investigated the two-step evaporation process of BaSi2 to fabricate the BaSi2 film capped with an a-Si layer on a Si(100) substrate. The deposition of Si is possible as the second step because a small amount of Si remains after the first BaSi2 evaporation step. Raman and X-ray photoelectron spectroscopies show that a-Si is formed by the two-step evaporation on the sample surface while Ba and carbonate species are not present on the surface, which are detected when the BaSi2 film is fabricated without the second step. Depth composition profiles determined by X-ray photoelectron spectroscopy clearly demonstrate the formation of the layered structure of a-Si and BaSi2. Owing to the a-Si capping, O concentration in the BaSi2 film is lower than that without a-Si, as evidenced by the composition profiles and energy-dispersive X-ray spectroscopy results. In addition, the microwave-detected photoconductivity decay analysis shows that the carrier lifetime in the a-Si/BaSi2 samples is similar to or slightly higher than the BaSi2 film without a-Si layer possibly due to the surface passivation effect and the reduction of oxygen concentration.