Effect of annealing treatment on microstructure and properties of porous silicon combined alumina coating film for silicon solar cells application

Aluminum oxide (Al₂O₃) nanoparticle films were prepared using a two-step process: resistive evaporation of an aluminum (Al) layer onto a porous silicon (PS) substrate, followed by thermal oxidation in an oxygen-rich atmosphere. The optical and microstructural characterization of the resulting films revealed that a minimum annealing temperature of 650 °C is required to achieve complete oxidation of the Al layer. X-ray diffraction (XRD) and Raman spectroscopy analyses confirmed the structural transformation of the films from metallic Al to Al₂O₃ at this annealing temperature. Optical measurements, including reflectivity (R), further support these findings, as only films annealed at 650 °C exhibited a significant reduction in R, indicating the successful formation of the Al₂O₃ phase. These results underscore the critical role of annealing temperature in tailoring the structural and optical properties of Al₂O₃ films for potential applications.