The optical properties of amorphous and crystalline germanium

Abstract

A detailed study has been made of Tomlin's method of determining the optical constants of an absorbing specimen by measuring the normal-incidence reflectances from the specimen itself and when coated with a thin transparent layer. It has been applied successfully to the measurement of the optical properties of amorphous and crystalline germanium in the spectral range from 700 to 300 nm where specimens are highly absorbing. For thin films it has thus been possible to extend the range previously covered by the reflectance and transmittance measurements of Denton and Tomlin (1972). The absorption of the amorphous thin films near the absorption edge has been re-examined and it is shown that four band gaps may be recognized, for which an interpretation in terms of a Mott-Davis (1971) model is offered.