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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The concentration dependence of the electron diffusion length in p-type GaAs is analyzed based on experiiiiental values reported in the literature and recent studies of minority carriers mobility in GaAs. The dependence of Ln with doping impurity concentration is determined for tllr > tr and good agreement is found with highest reported experimental values of Ln; considerations are rnatle about tnr. The dependence of electron mobility, diffusion constant, and radiative reconibination lifetime on concentration are also given.The importance of the knowledge of the values of the electron diffusion length in ptype GaAs is a well established fact.A

The dependence of the characteristic temperature T0 on the cavity length and lasing wavelength is theoretical and experimentally analyzed. The devices are straight separate confinement heterostructure lasers with active layer thickness of 30 and 12 nm grown by low temperature liquid phase epitaxy. The recent observation that for very short lasers T0 is an increasing function of the cavity length is confirmed, and explained in terms of the threshold current cavity length dependence. The temperature dependence of the threshold current Ith gives T0 as high as 307 K for a quantum well laser with cavity length L=168 μm.

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