Anomalous photoacoustic behavior of semiconductors: Evidence for thermally generated surface deformations

The photoacoustic signal measured for a solid sample is generally thought to originate from plane thermal waves, created by exposing the sample to modulated irradiation. For illumination of energy near or below the bandgap energy of a semiconductor, photoacoustic response was observed which could not be explained with conventional, thermal wave theory. This behavior can be explained if it is assumed that the signal is dominated by thermal deformations, generated at the semiconductor surface. This paper will show how this and other types of sample vibration can affect photoacoustic measurements of semiconducting materials.