Elimination of interference effects from photoinduced-transmission decay curves of thin silicon films

The effects of interference on the photoinduced-absorption signals of thin absorbing films have been studied by recording the picosecond photoinduced-absorption decay curves of an amorphous and a polycrystalline silicon film and applying various probe-beam wavelengths and angles of incidence. The normalized decay curves measured at close to normal incidence have been found to depend strongly on the probe-beam wavelength. By contrast the decay curves obtained at the Brewster angle of incidence have shown a satisfactory coincidence. Theoretical calculations for the photoinduced changes of the transmittance of the film have been performed. These calculations prove that at normal incidence the contributions of the photoinduced changes of the absorption coefficient Δα and of the refractive index Δn to the change in the transmittance Δ T are comparable, whereas when the Brewster angle arrangement is employed, Δ T is proportional to Δα and the effect of the change in the refractive index is negligible.