Long-Range Interaction in Multi-Layered Amorphous Film Structure

Long-range interactions in amorphous semiconductor have been studied by utilizing an amorphous As 40 Se 60 /Ge 25 Se 75 multi-layered film in which the average composition is kept constant. The optical gap shifts to higher energies as the layer pitch decreases. After passing a peak, it finally approaches that of mixed ternary film. This is discussed in terms of a one-dimensional quantum size effect. The photostructural change is not affected by multi-layered structure. Infrared absorption peaks, due to As–Se 3 and Ge–Se 4 molecular vibrations, shift to higher wavenumbers as the layer pitch decreases. This phenomenon can be described by using the built-in electric field, or coulomb force between As–Se 3 and Ge–Se 4 clusters, due to the electronegativity difference between As and Ge atoms. This is supported lay the oscillator strength change with the change in layer pitch.

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