A practical model for the determination of transport parameters in semiconductors

In this paper a new and practical model for the determination of transport parameters of crystalline semiconductors, by means of the photoacoustic technique is reported. The model is based on the calculation of the photoacoustic signal for the so-called heat transmission configuration, and considers that the thermal response to periodical heating, due to light absorption, in semiconductor materials has mainly two contributions: (a) the vibrations of the crystal lattice (phonon contribution) and (b) the diffusion and recombination (bulk and superficial) of the photogenerated charge carriers. Considering these contributions as the heat sources, and using unmixed Dirichlet and Neumann boundary conditions, the solution of the heat diffusion equation, necessary for the calculation of the photoacoustic signal is obtained. In addition, an expression-describing a particular transport regime-that can be used as practical fitting function, for the more available experimental conditions, is developed. Finally, values of transport parameters for silicon wafers are obtained by fitting this model to the experimental data, showing a good agreement with the values quoted in literature.