Transmission Properties of the Metal

All incident photons which generate electron hole-pairs within the semiconductor bulk and space charge regions must first pass through the semitransparent metal layer. Photons which are reflected at the air-metal interface or are absorbed within the metal do not contribute to the photo current. It is therefore of utmost importance that the transmittance of light into the semiconductor is made as high as possible. 

The theory of themulti layer optical problem of the SBSC structure has been described in the literature. For single layer dielectric coatings on silicon the optimum refractive index is 2.1 - 2.4. Coatings with refractive indices within this region lead to practically identical results with theoretical reflection losses as low at 6% for both Si and GaAs substrates. 

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