OPTICAL ASPECTS OF POROUS MC-SILICON UNDER HEAT TREATMENTS
M. S. BELKAID
The aim of this study is the formation of porous silicon (PS) and the heat treatment effect on the optical properties of the PS layer. An optimized HF:HNO3 chemical solution is used at ambient temperature on the n + p silicon surface. Scanning electron microscopy (SEM) pictures show the form of the nanopores. We studied the effect of the heating on the morphology and the reflection of the PS layer. A chemical analysis of the surface is also carried out. The measurements show that the pore shape and the oxygen content on the surface are changing with temperature. Specular reflection spectra under variable incidence angles are measured on each treated surface. Curves of weighted reflection Rw are drawn to illustrate the evolution with temperature. The modification of oxygen content of the porous surface is correlated with the sheet resistance of the emitter. Results show the lower the oxygen percent the lower the resistivity. The layout of Rw according to the temperature of annealing indicates that the shape of the curve is the same for the angles of incidences 20Â°, 30Â°, 40Â°, and 50Â°. At a low temperature Rw is minimal indicating the presence of an oxide coating on the porous layer an indication of optical adaptation between the air and the substrate of silicon.
Porous silicon, reflection, solar cell, heat treatment
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