Extension of the Rosencwaig–Gersho–Fernelius photothermal deflection spectroscopy model to account for multiple reflections in epitaxial samples

The Fernelius extension to the Rosencwaig–Gersho theory for photothermal deflection spectroscopy (PDS) is modified to take into account multiple reflections and light trapping within a thin film-on-substrate system where both the thin film and the substrate can be absorbing. The extended model is used to simulate the PDS signal from bulk GaAs and GaNAs epilayers grown on GaAs substrates. While the PDS magnitude signal shows a strong dependence on the light trapping effects, the phase signal remains almost insensitive to this effect. However, the PDS relative phase is very sensitive to the sample thickness.