Effect of Al2O3 Coatings on Microstructural and Optoelectronic Properties of Porous Si/ SnO2 Composites.

In this work, Al 2 O 3 coating effect on morphology, structure and optoelectronic properties of Si/SnO 2 /Al 2 O 3 porous matrix composites (PMCs) were investigated. A three-staked thin layers deposited on a ⟨100⟩ oriented silicon substrate made these composites. First, porous silicon layers were achieved by electrochemical etching method. Then Al 2 O 3 and SnO 2 layers were successively deposited by physical and chemical vapor deposition, respectively. Morphological and micro-structural properties of the as prepared composites were evaluated by Scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction. Results proved that Al 2 O 3 concentration alters notably the porosity of the PMCs.Variable angle spectroscopic ellipsometry (SE) revealed a high correlation between the optical constants (n, k) and the PMC microstructure. Impedance spectroscopy revealed a semiconductor-metallic transition at high frequency in the temperature range between 340 to 410°C.