Author: Lubomír Vančo

Raman spectroscopy of porous silicon substrates

Posted on by Lubomír Vančo

KADLEČÍKOVÁ, Magdaléna – BREZA, Juraj – VANČO, Ľubomír – MIKOLÁŠEK, Miroslav – HUBEŇÁK, Michal – RACKO, Juraj – GREGUŠ, Ján

In Optik. Vol. 174, (2018)

https://doi.org/10.1016/j.ijleo.2018.08.084

Abstract

We have investigated the effect of the etching time on the Raman spectra of porous silicon prepared by anodic etching. Electrochemical destruction of the substrate increasing with the etching time and the correlation between the microstructure of the silicon wafer and the shape and position of their Raman spectra have been observed. Raman analysis has shown that the intensity of the Raman dominant silicon band decreases and the bandwidth is shifted to lower frequencies, depending on the morphology of the sample. Therefore we believe that the electrochemical destruction of the surface of Si substrates leads to surface amorphization.

Oxidation-Induced Structure Transformation: Thin-Film Synthesis and Interface Investigations of Barium Disilicide toward Potential Photovoltaic Applications

Oxidation-Induced Structure Transformation: Thin-Film Synthesis and Interface Investigations of Barium Disilicide toward Potential Photovoltaic Applications

Posted on by Lubomír Vančo

TIAN, Yilei – VISMARA, Elena – VAN DOORENE, Steve – ŠUTTA, Pavol – VANČO, Ľubomír – VESELÝ, Marián – VOGRINČIČ, Peter – ISABELLA, Olindo – ZEMAN, Miro

In ACS Applied Energy Materials. Vol. 1, iss. 7 (2018)

https://doi.org/10.1021/acsaem.8b00486

Abstract

Barium disilicide (BaSi2) has been regarded as a promising absorber material for high-efficiency thin-film solar cells. However, it has confronted issues related to material synthesis and quality control. Here, we fabricate BaSi2 thin films via an industrially applicable sputtering process and uncovered the mechanism of structure transformation. Polycrystalline BaSi2 thin films are obtained through the sputtering process followed by a postannealing treatment. The crystalline quality and phase composition of sputtered BaSi2 are characterized by Raman spectroscopy and X-ray diffraction (XRD). A higher annealing temperature can promote crystallization of BaSi2, but also causes an intensive surface oxidation and BaSi2/SiO2 interfacial diffusion. As a consequence, an inhomogeneous and layered structure of BaSi2 is revealed by Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The thick oxide layer in such an inhomogeneous structure hinders further both optical and electrical characterizations of sputtered BaSi2. The structural transformation process of sputtered BaSi2 films then is studied by the Raman depth-profiling method, and all of the above observations come to an oxidation-induced structure transformation mechanism. It interprets interfacial phenomena including surface oxidation and BaSi2/SiO2 interdiffusion, which lead to the inhomogeneous and layered structure of sputtered BaSi2. The mechanism can also be extended to epitaxial and evaporated BaSi2 films. In addition, a glimpse toward future developments in both material and device levels is presented. Such fundamental knowledge on structural transformations and complex interfacial activities is significant for further quality control and interface engineering on BaSi2 films toward high-efficiency solar cells.