Abstract
Porous silicon (PSi) layers were formed on a p-type Si wafer. Electrochemical method was used to prepare 36 samples with three values of current density (10, 20 and 30) mA/cm2, each involved ( 20, 40, 60 and 80) min etching times the samples were heated to three selected temperatures of 100, 200 and 350°C in three groups. The first group covers 12 samples corresponding to 10 mA/cm2 while the other two correspond to the remaining values of current density respectively. Each annealing process for these sample groups lasted three hours in ambient air. The morphology of the layers, before and after annealing, formed by this method was investigated by Scanning Electron Microscope (SEM). Photoacoustic technique (PA) was employed carry out Thermal Diffusivity (TD) measurements. In this study, the porosity and thickness porous increased with increasing current density and etching time. While the thermal diffusivity TD increases with increasing annealing temperature.
Highlights
The principle of Photoacoustic (PA) effect has been studied for over a century
The result shown porosity in this experimental increased from 20.3 to 78.2% the thickness porous from 4 to 58.8 μm these results show that porosity was initially increased (Hussein et al 2015b) and the increment is found slow for porosity after 40 min because of the silicon structure is ready to porous and the porosity is high when the current density is higher
Temperature plays major important factor to change Thermal Diffusivity (TD) for the materials. In these experiments Porous silicon (PSi) samples were prepared by electrochemical method, the porosity is related to current density and etching time; the porosity increased when both are increased
Summary
The principle of Photoacoustic (PA) effect has been studied for over a century. The first phenomena of PA technique were first proposed by Alexander Graham Bell in 1880 (Favier, 1997). The PA effect in condensed matter may be detected by microphone by impinging modulated light on a solid sample surface which in turn produces heat on the sample surface. Rosencwing and Gersho (RG) derived a one-dimensional theory for the PA effect from a solid material, known as the R-G theory, which has formed the founding principles of other theories on microphone PA detection from solid sample (Rosencwaig and Gersho, 1976). RG theory one dimensional heat flow model has been greatly modified to form strong background platform for this technique (Aamodt and Murphy, 1981). RG theory for acoustic detection technique uses both gas condenser and microphone for pressure variation detection in air. According to RG theory, from the rear samples, the thermally thick PA signal amplitude decreases exponentially with modulation frequency as (Raveendranath et al, 2006):
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