Photoacoustic investigation of multilayer semiconductor materials

A one-dimensional model to investigate the photoacoustic (PA) generation and depth profiling in multilayer semiconductor materials has been developed by considering the contributions of thermal and plasma waves. The theoretical results show that the contribution of the plasma wave induced by photo-generated carriers (PGC) to the photoacoustic signal through the electro-elastic effect is predominant at high modulation frequencies and the contribution of the thermal wave, which is caused by the recombination of PGC, to PA signal through the thermo-elastic effect is more important at low modulation frequencies. We also investigated the depth profiling ability of PA detection by changing either the modulation frequency or the phase shift of the reference signal. The theoretical analyses are consistent with the experimental results.