Spectral absorption coefficient extraction of an unknown layer from photoacoustic measurements of multilayered semiconductors

摘要

This paper reports on a theoretical relation for the normalized photoacoustic amplitude signal for use in determining the optical absorption coefficient spectrum of any layer of multilayered semiconductors' samples. The derived relation is for use in gas-coupled photoacoustic cells. The model, unlike its predecessors so far reported in the literature that are usually for specific cases in dependence of the optical properties of the sample, takes into considerations the geometrical sample, the photoacoustic cell parameters, the thermal reflections as well as the light reflections at different interfaces. We present the results analysis on the effect of increasing the number of layers on the normalized photoacoustic response by considering particular applications in optoelectronic devices' configurations. A computer program has been developed to extract the absorption coefficient spectral distribution of any particular layer. Three specific experimental applications are provided in evaluating the performance of the present model. Unlike conventional spectroscopic techniques, the photoacoustic method is known for high delectability in the region of weak absorption. Hence, the applications we present here include the cases of a single transparent sample, a thin solid single crystal and embedded layer in a three-layered sample.