Thickness dependence of optical gap and absorption tail for amorphous germanium films

Abstract The optical constants of four dc-magnetron sputtered a-Ge films with different thicknesses have been determined. From optical absorption, a thickness dependence of optical gap and absorption tail has been found, and it is associated with different void fractions in the films, that could induce a downward movement of the valence band with respect to the defect states and the conduction band. Oxygen depth profiles, carried out on the films, support a thickness dependence of the film void fraction, due to a gradient in the void density which suggest a cone growth for our films.