THE PHOTOACOUSTIC EFFECT IN POROUS SILICON - PECULIARITIES OF ITS MANIFESTATION AND ITS APPLICATION TO THE INVESTIGATION OF OPTICAL AND THERMAL-PROPERTIES OF MATERIALS

The peculiarities of the manifestation of the photoacoustic effect in porous Si are studied using a gas-microphone and piezoelectric signal detection techniques. It is shown that in porous Si samples irradiated with short laser pulses, apart from bright visible luminescence, very efficient sound generation is also observed. The possible mechanisms giving rise to the anomalously high efficiency of sound photogeneratio n in porous Si are analysed. The results of the studies of photoacoust ic response as a function of wavelength and frequency of modulation of excitation light are also presented, along with luminescence spectra taken at various time delays for the same samples. These results have made it possible to determine the position of the optical absorption e dge of 'filaments' in the structure of porous Si and also the average value of thermal diffusivity for porous Si layers. Conclusions are giv en regarding spatial localization and relaxation of energy of the 'osc illators' responsible for visible luminescence of the porous Si.