In situ photoacoustic characterization for porous silicon growing: Detection principles

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.

Modeling the photoacoustic signal during the porous silicon formation

“…It is suggested the Ref. 9 for a more detailed description of the electrochemical PA experimental setup. …”

Optical interferometry and photoacoustics as in-situ techniques to characterize the porous silicon formation: a review

“…The electrochemical cell (two electrodes configuration) was coupled with an open photoacoustic cell [24]. In this kind of configuration, the incident radiation comes from the front, and the sensor ( e.g., piezoelectric transducer [22,23] or electret microphone [24,25]) is located at the back of the Si substrate.…”

“…In this kind of configuration, the incident radiation comes from the front, and the sensor ( e.g., piezoelectric transducer [22,23] or electret microphone [24,25]) is located at the back of the Si substrate. A p-type Si is usually used because the I-V curve does not change as a function of the lighting conditions.…”

“…The main techniques reported to study the in situ formation of PSi by electrochemical etching in hydrofluoric acid(HF) media are: in situ Fourier transform infrared spectrometry (FTIR) [10,11], optical interferometry [12][13][14][15][16][17] optical scattering [19,20], and photoacoustics [21][22][23][24][25].…”

“…It is useful to follow changes in optical and thermal properties in real time, the formation of multilayers, wetting process [21] , emptying and filling of porous media, and chemical reactions. Indeed, it is possible to perform an in situ monitoring of the PSi formation by using photoacoustic in HF aqueous media [21][22][23][24][25].…”