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 pho toinduced-absorption decay curves of an amorphous and a polycrystallin e 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 wavelen gth. By contrast the decay curves obtained at the Brewster angle of in cidence have shown a satisfactory coincidence. Theoretical calculation s for the photoinduced changes of the transmittance of the film have b een performed. These calculations prove that at normal incidence the c ontributions of the photoinduced changes of the absorption coefficient Delta alpha and of the refractive index Delta n to the change in the transmittance Delta T are comparable, whereas when the Brewster angle arrangement is employed, Delta T is proportional to Delta alpha and th e effect of the change in the refractive index is negligible.