Thermal characterization of n-type silicon based on an electro-acoustic analogy

Abstract

Based on the analogy between resistor-capacitor (RC) filters and the thermoelastic component of a photoacoustic signal, the complex thermoelastic response of an open photoacoustic cell is described as a simple linear time-invariant system of a low-pass RC filter. This description is done by finding a linear relation between the thermoelastic cut-off frequency and sample material thickness within the range of 10-1000 μm. Based on the theory of a composite piston, we run numerical simulations of the proposed method for n-type silicon, described as either a surface or volume absorber. Theoretical predictions are experimentally validated by using an open photoacoustic cell setup to record the signal of an 850-μm-thick n-type silicon wafer illuminated by a blue light source modulated with frequencies from 20 Hz to 20 kHz. The obtained experimental results confirm the linear dependence of the thermoelastic cut-off frequency on the sample thickness, and, therefore, they lay the foundation of a new method for the thermal characterization of materials. © 2023 Author(s).