With the recent development of an electropolishing technique for producing optically smooth and flat surfaces with a minimum amount of surface damage, a quantitative study of the influence of surface damage and lattice disorder on the optical properties of semiconductors has become possible. In this investigation precise absolute specular reflectance measurements at normal incidence are reported for electropolished and mechanically polished germanium single crystals and for amorphous and polycrystalline germanium films in the 2650-10 000-Å wavelength range. The highest reflectance maxima and considerable structure were exhibited by the electropolished sample. Splitting of the 2.1-eV peak, which had previously been reported only for etched samples, was observed, and shoulders at 3.25 and 2.47-eV were found. The latter shoulder has apparently not been reported previously. The wavelength at which the 2.1-eV peak occurred shifted for the mechanically polished single crystal and for the polycrystalline film and disappeared entirely for the amorphous film. However the 4.4-eV peak, although changing greatly in magnitude, occurred at the same wavelength for all the samples tested. The results of the experiment show that the optical properties of this material are a strong function of the lattice disorder present and emphasize the importance of adequate sample preparation techniques if meaningful optical measurements are to be made.
T. M. DONOVAN, E. J. ASHLEY, and H. E. BENNETT, "Effect of Surface Damage on the Reflectance of Germanium in the 2650-10 000-Å Region," J. Opt. Soc. Am. 53, 1403-1408 (1963)