In this work, we report a study of the optical properties measured through spectral transmission and spectroscopic ellipsometry in Ge:H and Ge gamma Sil-Y:H (Y approximate to 0.97) films deposited by low frequency (LF) PE CVD with hydrogen (H) dilution. The dilution was varied in the range of R=20 to 80. It was observed that H-dilution influences in a different way on the interface and bulk optical properties, which also depend on incorporation of silicon. The films with low band tail characterized by its Urbach energy, E-U, and defect absorption, alpha(D), have been obtained in Ge:H films for R=50 with E-U=0.040 eV and alpha(D)=2 x 10(3) cm(-1) (h nu approximate to 1.04 eV), and in Ge gamma Sil-Y:H films for R=75 with E-U=0.030 eV and alpha(D)=5 x 10(2) cm(-1) (hv approximate to 1.04 eV). (c) 2006 Elsevier B.V. All rights reserved.