Evaluation of Multilayer Structure by Using new High Sensitivity PAS

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We developed a PAS (Photoacoustic Spectroscopy) using a transparent transducer. It is possible to evaluate an absorption coefficient of semiconductors quantitatively and to perform a reproducible experiment. As the light can irradiate through a transparent transducer, a generated acoustic slignal is directly detected by this transducer. Consequently, the sensitivity is considerably improved and there are no sample geometry limitations. Especially, this method is effective to evaluate the surface layer of the samples, ion implanted layers, interface of heteroepitaxial layers, and so on.1. It is so sensitive that it is possible to detect the signals from the ion implanted layer. As this layer is so thin (900-3200, *) that this method is also applicable to evaluate the surface damages of semiconductors.2. At low energy region we could detect a weak absorption which is generated by the localized states of ion implanted layer. By estimating this value, it is possible to evaluate the recovery process of the thin ion implanted layer by thermal annealing, quantitatively.Next, PA signals from GaInP/GaAs heterostructure and multilayer structures of semiconductors were observed and the following results were obtained.3. Each absorption edge of multilayer structure is determined separately by the PA dips and large phase shift.4. Nonradiative defects are detected clearly at GaInP/GaAs interface.5. The PA dip occurs at interfacial layer when the signal origin moves from one to another layer as irradiated wavelength changes. This is because the transducer detects two different phase signals with different amplitudes of each layer at the same time.6. Now we are trying to separate the signals from piezoelectric and piroelectric effects and to make it possible to evaluate the optical and thermal constants quantitatively by comparing with the theoretical analysis.