Vibrational Raman studies of amorphous solid interfaces

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Abstract
We report and quantitatively analyze vibrational Raman spectra of (hydrogenated amorphous silicon)–(silicon nitride) and silicon-germanium interfaces. Periodic multilayer structures were deposited by plasma-assisted chemical-vapor deposition with layer repeat distances from 1.5 to 20 nm. The repeat distance was varied in order to vary the fraction of the multilayer structure which is near the interface between the two materials and thereby separate interface vibrational structure from bulk properties. We find significant distortions in amorphous silicon material near the silicon–(silicon nitride) interface with estimated deformation energy of almost 1 eV per silicon atom. This distortion could be due either to interface strain from network mismatch or to incorporation of excess nitrogen in the a-Si near the interface. The distortion is confined to within two monolayers of each interface. No excess deformation is found near the silicon-germanium interface. We also report the observation of size effects on the optical properties of a-Si:H using resonant Raman scattering.