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Structural, Morphological and Electrical Properties of Porous Silicon Prepared Under Laser Illumination

Porous silicon (PSi) layers has been prepared in this work via photoelectrochemical (PEC) etching process of an n type silicon wafers of two resistivities (3.5 ohm.cm and 0.02 ohm.cm) in hydrofluoric (HF) acid of 24.5 precent concentration at different etching times (5 to 25 min). The irradiation has been achieved using laser beam of 2W power and 810 nm wavelength. We have studied the morphological and structural properties of PSi layers using the techniques of Xray Diffraction (XRD) and Scanning Electron Microscopy (SEM) and Gravimetric method. The Xray Diffraction data shows that the structure aspect of PSi layers remains crystalline as well as the decreasing of diffraction angle (thetaB) of Xray from PSi layers (29 to 26 degree) and increasing of the lattice parameter values of PSi structures with increasing of etching times from 5 to 25 min., and the resistivity of silicon substrates from 0.02 to 3.5 ohm.cm. The nanocrystallite size is decreasing from (20.72 to 5.13 nm) with increasing of etching times, and the resistivity of silicon substrates. The SEM images shows that the values of pore width and PSi layer thickness increases from (0.5 to 6.25 micrometer) and (6.7 to 47 micrometer) respectively with increasing of etching times and silicon substrates resistivities, while the values of the thickness of walls between pores has been varied from (1.25 to 0.03 micrometer) with increasing of etching times and silicon substrates resistivities. The pore shape of pores has been varied from Cylindrical to Rectangular and to Starful with varied of etching conditions. Further the measured specific surface area of PSi layers has been increased from (7.43 to 235.35 m2/cm3) with increasing of etching times and silicon substrates resistivities.