The interplay between plasma and thermal transport phenomena in semiconductors under optical excitation is fundamental to optoelectronics and forms the physical basis of photothermal and photoacoustic techniques. In this work, we develop a comprehensive one-dimensional multi-physics model that describes the coupled spatiotemporal dynamics of photogenerated charge carriers and heat transfer in a crystalline silicon (Si) wafer surrounded by air. The model consistently couples photogeneration, diffusion, and recombination of charge carriers with heat generation arising from carrier thermalization and from non-radiative bulk and surface recombination processes. The theoretical framework is based on the ambipolar diffusion equation within the low-level injection approximation for the carrier plasma, combined with heat conduction equations governing the temperature distribution in the illuminated sample. Time-domain simulations under rectangular optical pulse excitation reveal distinct dynamic regimes governed by the relation between the pulse duration and the characteristic plasma rise time. We identify the physical origin of key temporal features of the thermal response, including surface-localized thermal overshoot, and quantify the separation between fast plasma kinetics and slow thermal diffusion. The results provide a unified physical framework for interpreting time-resolved photothermal and photoacoustic signals in semiconductors and offer practical guidelines for experiment design and signal analysis.
Todorović et al. (Mon,) studied this question.