Amorphous silicon as a selective absorber of solar energy: a spectral emissivity study

A method for the measurement of the thermal emissivity of films on substrates and for the subsequent determination of the optical constants is described. It is applied to sputtered amorphous silicon films on sapphire substrates. The results, obtained in the 3-6.3-microm spectral range and at 400-800 degrees C, confirm the existence of residual ir absorption in this region with an absorption coefficient on the order of 10(2).