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Abstract In this paper we present an extensive investigation of the effect of Ni metallization on the structural and opto-electronic properties of a dual porous silicon layers elaborated by electrochemical etching. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on the metalized porous layer. The microstructure of porous silicon films was systematically studied by atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). It was found that the structure of the porous layer metalized Nickel (Si p MNi) strongly depends on the porosity level and on the immersion time in the Ni solution. The optical constants (n and k as a function of wavelength) of the Si p MNi were obtained using variable angle spectroscopic ellipsometry (SE) in the UV–vis–NIR regions. The SE spectrum of the SipMNi was modeled as a mixture of void, crystalline silicon and Ni nanoparticles using the Cauchy model approximation. The electrical conductivity, conduction mechanism, relaxation model of the Si p MNi/Si samples were studied by means of the impedance spectroscopy technique at various temperatures (340–410 °C). At high frequency a semiconductor to metallic behavior transition has been observed. A full correlation between the microstructure and opto-electrical properties has been presented. It was found that this simple and easy method is effective to produce silicon thin films with high quality suitable for opto-electronic applications. Highlights • Dual porous silicon layers are elaborated by electrochemical etching. • Effect of nickel coated porous Si on the Si thin films properties is investigated. • The optical constants (n and k) of the Si p MNi were obtained by spectroscopic ellipsometry (SE). • Electrical conductivity and conduction mechanism were studied by impedance spectroscopy. [ABSTRACT FROM AUTHOR]

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 and 410 °C. [ABSTRACT FROM AUTHOR]

In this work, nanocrystalline silicon (nc-Si) are deposited in a porous anodic alumina (PAA) matrix by a radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method. The rapid thermal annealing (RTA) effect on morphological and microstructural properties of nc-Si/PAA structure is investigated by SEM, EDX, XRD technique and Raman spectroscopy. Crystallization of the amorphous silicon is obtained after annealing at was 550 °C during a time ranging from 10 to 120 min. The effect of thermal annealing on the optical properties of nc-Si/PAA structure was studied by Spectroscopic Ellipsometry (SE) in the spectral range 0.3–0.8 μm. The Ellipsometric analysis demonstrated the formation of two separate layers during the annealing process. A silicon/alumina alloy as the upper layer and a polysilicon film at the bottom and in contact with the alumina barrier layer. The optical constants, thickness and the composition of each film have been estimated from the SE data using Bruggeman effective medium approximation (BEMA). PL spectroscopy was used to investigate the bandgap energy of nc-Si embedded within the PAA matrix, the origin of emission PL spectra as well as the observed red-shift have been discussed. [ABSTRACT FROM AUTHOR]