Refractive indexes of amorphous boron films prepared by plasma deposition

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Abstract

Studies were made of low frequency refractive indexes for pure and hydrogenated amorphous boron films prepared by plasma deposition. The refractive indexes were measured by interference fringes. It is shown that the refractive indexes vary widely depending on the deposition conditions and sometimes have larger values compared with the crystal. Next, absorption spectra were examined at energies below 6 eV. Comparison of the absorption spectra leads to the following explanation of these features. In pure a-B, the absorption near the band edge is stronger than in the crystal and varies widely, while conventional definitions of the gap give nearly constant values which are slightly smaller than the crystalline gap. As a consequence, it seems reasonable that the refractive indexes of the amorphous phase are likely to be larger than that of crystalline boron. For a-B:H, the variation in the gap is rather clear and can contribute to the variation in the refractive indexes, the effect of which may be regarded as an essential modification of the matrix by the hydrogen incorporation. A brief discussion is given of theoretical models of the refractive indexes of this system.

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