ON THE THERMAL CHARACTERIZATION OF 2-LAYER SYSTEMS BY MEANS OF THE PHOTOACOUSTIC EFFECT

In this work, the problem of the thermal characterization of two-layer systems by means of the photoacoustic technique is discussed. For a t wo-layer system under rear-side illumination conditions, we have appli ed the Rosencwaig and Gersho model for calculating the pressure fluctu ation in the photoacoustic gas chamber. The limiting cases in which bo th layers are thermally thin, thermally thick and one layer is thermal ly thin and the other is thermally thick are discussed. When both laye rs 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 res ults, we apply them to two-layer systems consisting of AlGaAs layers o f different Al concentrations, grown by liquid phase epitaxy on GaAs s ubstrates. 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 sys tems reported by Mansanares et al (1990 Phys. Rev. B 42 4477).