In situ photoacoustic characterization for porous silicon growing: detection principles

TL;DR

This paper explains the physical origin of photoacoustic signals during porous silicon formation and proposes a method to determine key properties like etching rate and porosity using in-situ photoacoustic measurements.

Contribution

It provides a physical explanation for the photoacoustic signal during PS etching and introduces a methodology to determine PS properties via signal analysis and SEM imaging.

Findings

Photoacoustic signal period is proportional to laser wavelength.

Method can determine etching rate, porosity, and refractive index.

Periodic photoacoustic signals correlate with etching process.

Abstract

There are a few methodologies to monitoring the Porous Silicon (PS) formation in-situ. One of these methodologies is photoacoustic. Previous works that reported the use of photoacoustic to study the PS formation do not provide the physical explanation of the origin of the signal. In this paper, a physical explanation is provided of the origin of the photoacoustic signal during the PS etching. The incident modulated radiation and changes in the reflectance are taken as thermal sources. In this paper, a useful methodology is proposed to determine the etching rate, porosity, and refractive index of a PS film by the determination of the sample thickness, using SEM images. This method was developed by carrying out two different experiments using the same anodization conditions. The first experiment consisted of the growth of samples with different etching times to prove the periodicity of the photoacoustic signal and the second considered the growth samples using three different wavelengths that are correlated with the period of the photoacoustic signal. The last experiment showed that the period of the photoacoustic signal is proportional to the laser wavelength.