Electron and phonon thermal waves in semiconductors: the effect of carrier diffusion and recombination on the photoacoustic signal

Abstract

The electron and phonon temperature distributions are calculated in bipolar semiconductors by taking into account generation and heating of carriers on the surface due to the incident modulated laser beam as well as the finite carrier diffusion and recombination in the solid. We solve the coupled one-dimensional heat and carrier diffusion equations in the linear approximation using appropriate boundary conditions according to the photoacoustic experimental conditions. In addition, special emphasis is laid on the dependence of the electron system heat flux on the electron and phonon temperature. We also consider the influence of both temperatures on the recombination of the electron–hole pairs. The dependence of the amplitude of the electron and phonon temperatures on the modulation frequency are analyzed for different values of characteristic parameters of the problem: electron–phonon energy exchange and carrier thermal generation rate.