The Influence of Excess Free Carriers as Heat Carriers on the n-Type Silicon Thermoelastic Photoacoustic Responses Explained by Electro-Acoustic Analogies

The explanation of the n -type silicon thermoelastic photoacoustic response is given by electro-acoustic analogies, which clarify the influence of excess free carriers as heat carriers. It was found that electro-acoustic analogies could interconnect different theoretical models of heat flow and carrier dynamics aiming to find the optimal experimental conditions for the efficient free carrier influence analysis of the sample thermoelastic photoacoustic response. Theoretical analysis was based on the comparison between the composite piston, surface recombination, and RC filter frequency response models, extrapolating the behavior of the photoacoustic response much beyond the experimental frequency domain. Experimental analysis was based on the open-cell photoacoustic setup operating under the transmission configuration within the modulation frequencies range from 20 Hz to 20 kHz. The accuracy of our predictions and the validity of electro-acoustic analogies are confirmed by measuring 875 μm plasma-thick and 35 μm plasma-thin silicon samples.