Salnykov V. Photoacoustic spectroscopy of nanoscale semiconductor structures

The thesis is devoted to study of properties of semiconductor structures, containing quantum dots, by means of photoacoustic (PA) spectroscopy technique. It is shown at the first time that effect of generation of sound of giant intensity is peculiar to the systems of thermally insulated light-absorbing particles. The nature of this phenomenon is explaned by local overheating of photoexited particles and subsequent relaxation of thermal energy through the generation of elastic oscillations. The correlation between density of dielectric matrix and some peculiarities of PA spectral and frequency dependences is discovered. The origin of such behavior in the case of porous sample has been explained by contribution from interstitial (i.e. contained inside the pores of sample) gas into the total photoacoustic signal. Also, the effect of blue shift of absorption edge for CdS and PbI2 nanophases is observed. The effect is explained as a manifestation of the quantum-size effect in energy spectrum renormalizationin investigated structures if compared with corresponding bulk materials. A new technique for thermal diffusivity coefficient determination is proposed. Using this technique we have shown that the thermal diffusivity is a measure of porosity of material and for samples of por-Si with porosity of 70 % the thermal diffusivity value is equal to corresponding value of SiO2 layers. All the results obtained extend the understanding of physical processes inside the ensemble of photoexcited semiconductor nanoparticles and confirm the perspectives of using the PA-spectroscopy as a methodical base for studying of this class of materials.