Enhancement of the thermoelastic component of the photoacoustic signal of silicon membranes coated with a thin TiO2 film

The reduction of the photogenerated charge carriers' influence in periodically illuminated thin silicon membranes is investigated by using the experimental setup of an open photoacoustic cell in the standard range of modulation frequencies from 20 Hz to 20 kHz. It is confirmed that the deposition of a 200 nm thin film of titanium dioxide on the 30- and 50 mu m silicon membrane leads to a large increase of the thermoelastic component of the photoacoustic signal, which restores the flexibility lost to the membrane under the influence of photogenerated carriers. The effect of the thermoelastic component enhancement is analyzed by observing the displacement of the tested samples along the heat propagation axis, depending on the carrier density and temperature differences on the illuminated and unilluminated sides, for different membrane thicknesses and a constant film thickness. It is found that the effect of enhancement of several orders of magnitude is more visible in thinner membranes due to higher ratios between the film and membrane thicknesses.

Automated summary

This study investigates the reduction of the influence of photogenerated charge carriers in periodically illuminated thin silicon membranes. It is found that the deposition of a titanium dioxide thin film can increase the thermoelastic component of the photoacoustic signal and restore the flexibility of the membrane. The effect is more significant in thinner membranes.