Silicon powder-based wafers for low-cost photovoltaics: laser treatments and nanowire etching
in: International Journal of Photoenergy (2018)
In this study, laser treated polycrystalline-Si (pc-Si) wafers, fabricated by wire sawing of hot pressed ingots sintered from Si powder have been investigated. As-cut wafers and those with high quality thin Si layers deposited on top of them by e-beam, have been subjected to laser irradiation to clarify typical trends of structural modifications caused by laser treatments. Moreover, possibility to use laser treated Si powder based substrates for fabrication of advanced Si structures has been analysed. It is established that: (i) Si powder based wafers with thicknesses ~180 µm can be fully (from the front to back side) or partly (sub-surface region) re-melted by diode laser and grain sizes in laser treated regions can be increased; (ii) a high quality top layer can be fabricated by crystallization of an additional a-Si layer deposited by e-beam evaporation on top of the pc-Si; (iii) silicon nanowires can be formed by metal assisted wet chemical etching (MAWCE) of polished Si powder based wafers and as-cut wafers irradiated with medium laser power, while a surface texturing on the as-cut pc-Si wafers occurs, and no nanowires can form in the region subject to a liquid phase crystallization (LPC) caused by high power laser treatments.