Experimental photoacoustic observation of the photogenerated excess carrier influence on the thermoelastic response of n-type silicon

Abstract

Based on the experimental and theoretical signals of an open photoacoustic cell operating with modulation frequencies from 20 Hz to 20 kHz, a significant contribution of photogenerated excess carriers on the thermal and thermoelastic responses of an n-type silicon plate is observed for the very first time. This is achieved by comparing the measured amplitude and phase of the photoacoustic signal with their corresponding theoretical thermoelastic counterparts, for high enough modulation frequencies mainly. It is shown that the amplitude of the thermoelastic component of plasma-thin samples varies about two orders of magnitude with respect to the corresponding one of plasma-thick samples. Furthermore, we find a maximal temperature difference ΔT = − 35 nK between the illuminated and non-illuminated sample surfaces, which shows that thin silicon plates with excess carriers could be used as heat sinks.

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

“…It was observed that the influences of carriers on the thermal response are most intense in semiconductor membranes having the shape of circular plates with a thickness smaller than the sample carrier diffusion length (so-called plasma-thin samples). A strong decrease in the amplitude of the thermoelastic component and a decrease in the total phase of the photoacoustic signal was observed as a typical pattern of the PA signal behavior in the frequency domain [13,14]. In practical terms, it means that the degree of bending of the illuminated semiconductor membrane decreases under the influence of photogenerated carriers.…”

“…The photoacoustic response of the two-layer sample irradiated with the modulated light source (Figure 1) [16,17,20] can be theoretically described by the total PA signal ( ) total pf  defined with the simple equation [13,14]:…”

“…are the thermal diffusion (TD), thermoelastic (TE) and plasma elastic (PE) PA signal components, respectively. Using a simple 1D theoretical model [13,16,17,20] these components can be written as:…”

“…There are various spectroscopic methods within photothermal sciences that can be used to analyze such thermal responses [6][7][8][9][10][11][12]. In our previous articles [13][14][15], we showed that photoacoustics (PA) is a method by which different thermal responses of semiconductors can be clearly observed under the strong influence of photogenerated carriers, by analyzing different patterns of behavior of photoacoustic signals and their components. It was observed that the influences of carriers on the thermal response are most intense in semiconductor membranes having the shape of circular plates with a thickness smaller than the sample carrier diffusion length (so-called plasma-thin samples).…”

Development and Comparison of the Techniques for Solving the Inverse Problem in Photoacoustics

“…being thermal diffusion length of the semiconductor and T D being thermal diffusivity, while the integration constants Comparing the prediction of the abovementioned model to the experimental measurements on 150µm thick Silicon sample, it is shown that TMS model matches the experiment only in the (50Hz -2kHz) frequency range. Notable difference at low and at high frequencies is attributed to the influence of the noise and to the influence of the measurement chain, so the utilization of the whole frequency measurement range demands detailed analysis and the elimination of these influences (Djordjevic et al 2020a;Jordovic-Pavlovic et al 2020;Markushev et al 2020;Pavlović et al 2019). In this paper, inverse solving procedures are developed on a limited frequency range, aiming at the determination of silicon properties with dominant influence in the mentioned range, namely the coefficient of thermal diffusion and linear thermal expansion coefficient.…”