Interference enhanced Raman scattering of hydrogenated amorphous silicon revisited

We report interference enhanced Raman scattering (IERS) of very thin and highly absorbing (α > 10⁵ cm^-1) device-quality hydrogenated amorphous silicon (a-Si:H) films. The IERS technique, in general, can give a gain of 10-10³, depending on the optical constants of the material. The potential of this method is demonstrated experimentally using device-quality a-Si:H films at a wavelength of 514 nm. IERS is shown to produce an intensity gain (G) of 50 in the scattered intensity of a thin (19 nm) a-Si:H film as compared with the poor signal obtained for a thick specimen (1 μm) using conventional Raman scattering in backscattering configuration. The TA- and TO-like signatures of the enhanced spectra stand out clearly, thus being suitable for the structural characterization of this material. It is also shown that the intensity enhancement effect decreases when the incident radiation wavelength is changed to 604 nm, thus deviating from the required interference condition. IERS can have important applications in the study of many materials, such as metals, metallic alloys, semiconductors and surface adsorbates.