NOVEL PHOTOACOUSTIC-SPECTROSCOPY OF SEMICONDUCTOR THIN-FILMS BY A TRANSPARENT TRANSDUCER - PYROELECTRIC AND PIEZOELECTRIC EFFECTS

We have studied the generation mechanism of photoacoustic (PA) signals in semiconductor thin films by means of a transparent LiNbO3 transducer both experimentally and theoretically. In the transparent transducer method, the PA signal was detected at the light-irradiated surface of the samples. The PA signal of the thin film directly attached to the transducer is mainly due to the pyroelectric effect, and the PA signal of the underlain substrate is the piezoelectric signal caused by sample bending. These results show that this method becomes a powerful tool for measuring optical and thermal properties of thin films on the substrate nondestructively.