**1. Introduction**

Porous silicon has undergone many developments; it has a very wide field of application and has received a great deal of attention from researchers because of its potential use in a variety of industrial applications such as photovoltaic device applications [1–4], chemical and gas sensors [5–12], biosensors [13, 14], biomedical applications [15], micromachining [16–18], templates for micro- and nanofabrication [19–21], and solar cells and photoluminescence [1, 22, 23]. However, a very limited data of optoelectronic uses in this field are available [24, 25]. It is reported that the photoluminescence of porous silicon (PS) has achieved a largescale investigation, giving an explanation of the photoluminescence phenomenon with obtaining the optical properties of porous silicon, as well as determining its refractive index and the gap energy, which can be determined directly by the absorption measurement, or by a non-destructive technique called spectroscopic ellipsometry (SE).

However, the physical and optical properties could be studied. In addition, some of the physical phenomena are still poorly understood because of the strong relationship between the PS nanostructure and the elaboration conditions (HF concentration, current density, and anodization time) [26]. The present study conclusively suggested that in order to prepare porous silicon samples, we need to determine the optimal conditions that lead to increase the optical efficiency. Herein, we need to study the correlation between the results extracted from the PL analysis and those obtained by ellipsometry. The study of the evolution of the intensities of the emission spectra obtained by the measurement of PL as a function of the porosity and the thickness determined by the ellipsometry of the layers for silicon substrates oriented P-100 of low resistivity is made to precisely clarify the evolution of optical parameters.
