Photoacoustic study of the electron–hole transport in a piezoelectric semiconductor

Abstract

In a piezoelectric semiconductor acoustic waves can be excited via the inverse piezoelectric effect. This excitation process is the result of a screening of the applied electric field by the expanding space distribution of electrons and holes which are generated by pulsed laser radiation. The time and space characteristics of the electron–hole transport in this process are contained in the corresponding acoustic signals. The piezoelectric direct-gap semiconductors cadmium sulfur selenide and gallium arsenide are investigated experimentally at room temperature. A pulsed nanosecond UV excimer laser is used to excite electrons and holes on these samples. The generated longitudinal acoustic waves are detected by a laser interferometer. The obtained acoustic pulses of cadmium sulfur selenide show that both the expansion of the screened region in space and the electron–hole plasma expansion are supersonic at the time scale of laser action. The observations in this optoacoustic experiment indicate that the fast carrier transport is governed by photon recycling, i.e., the reabsorption of photons released by radiative recombination of electron–hole pairs. Experiments for gallium arsenide are in progress and will also be reported.