Optical Properties of Thin Germanium Films

Abstract

The refractive and absorption indices of thin amorphous germanium films have been obtained from measurements, at normal incidence, of reflectances and transmittances over a wide range of wavelengths. The optical constants derived were in general agreement with the results of Tauc et al. (1964) except in the long wavelength region beyond the absorption edge. The absorption followed the law for indirect transitions from 0·72 to 1·1 eV, and the same law, but with a change in the slope of the curves, from 1·1 eV to the limit of our measurements at about 1·5 eV. The results are consistent with the view that the energy band structure of amorphous germanium is not essentially different from that of the crystalline material, except that the random structure eliminates the restriction that allows only direct transitions with the result that the absorption law for amorphous films is of the same form as for indirect transitions in crystals.