Optical and electrical properties of nonstoichiometric a-Ge1-xCx films prepared by magnetron co-sputtering

Amorphous non-hydrogenated germanium carbide (a-Ge1-xCx) films have been prepared by magnetron co-sputtering method in a discharge of Ar. The dependence of structural and chemical bonding properties on the Ge/C ratio (R) has been investigated by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The relationship between the chemical bonding and the optical and electrical properties of the a-Ge1-xCx films has also been explored. It has been shown that the refractive index of the films increases from 2.9 to 4.4 and the optical gap decreases from 1.55 to 1.05 eV as R increases from 1.22 to 5.67. Moreover, the conductivity sigma increases clearly and the activation energy E-a decreases with the increasing R owing to the reduction of sp(3) C-Ge bonds. The a-Ge1-xCx films exhibit refractive index and optical gap values changing with x in a wide range, which may make a-Ge1-xCx films good candidates in the fields of protection coatings for IR windows and electronic devices. (C) 2011 Elsevier B.V. All rights reserved.