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In this work, the problem of the thermal characterization of two-layer systems by means of the photoacoustic technique is discussed. For a two-layer system under rear-side illumination conditions, we have applied the Rosencwaig and Gersho model for calculating the pressure fluctuation in the photoacoustic gas chamber. The limiting cases in which both layers are thermally thin, thermally thick and one layer is thermally thin and the other is thermally thick are discussed. When both layers are thermally thin, a consistent equation for the heat capacity is obtained and an effective thermal diffusivity equation is derived when both layers are thermally thick. In order to test our theoretical results, we apply them to two-layer systems consisting of AlGaAs layers of different Al concentrations, grown by liquid phase epitaxy on GaAs substrates. The results of our measurements are in good agreement with the theoretical predictions. Our results show the general character of the expression for the effective thermal diffusivity of two-layer systems reported by Mansanares et al (1990 Phys. Rev. B 42 4477).

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