Thickness-dependent void fraction of rf-sputtered amorphous Ge films by spectroscopic ellipsometry

In this letter it is shown that vapor deposited thin films prepared under conditions of low adatom mobility, such as amorphous Ge films in the present study, exhibit a nonlinear decrease in void fraction, and hence an increase in density with increasing film thickness. Fractal modeling of the internal void network structure in this class of vapor deposited films shows that the void boundaries define the surfaces of growth cones and these voids are, in general, not expected to be distributed uniformly with film thickness.