The coefficient of thermal expansion ͑CTE͒, biaxial modulus, and stress of some amorphous semiconductors ͑a-Si:H, a-C:H, a-Ge:H, and a-GeC x :H͒ and metallic ͑Ag and Al͒ thin films were studied. The thermal expansion and the biaxial modulus were measured by the thermally induced bending technique. The stress of the metallic films, deposited by thermal evaporation ͑Ag and Al͒, is tensile, while that of the amorphous films deposited by sputtering ͑a-Si:H, a-Ge:H, and a-GeC x :H͒ and by glow discharge (a-C:H) is compressive. We observed that the coefficient of thermal expansion of the tetrahedral amorphous thin films prepared in this work, as well as that of the films reported in literature, depend on the network strain. The CTE of tensile films is smaller than that of their corresponding crystalline semiconductors, but it is higher for compressive films. On the other hand, we found out that the elastic biaxial modulus of the amorphous and metallic films is systematically smaller than that of their crystalline counterparts. This behavior stands for other films reported in the literature that were prepared by different techniques and deposition conditions. These differences were attributed to the reduction of the coordination number and to the presence of defects, such as voids and dangling bonds, in amorphous films. On the other hand, columnar structure and microcrystallinity account for the reduced elasticity of the metallic films.

Optoelectronic, structural, and mechanical properties of hydrogenated amorphous germanium carbon (a-Ge 1Ϫx C x :H) alloys are presented. The films were prepared by the rf cosputtering technique using graphite-germanium composite targets. Films with carbon contents in the 0Ͻx Ͻ1 range were prepared under the same conditions used to obtain a-Ge:H films with good optoelectronic properties. The trends of the optical gap, infrared absorption, dark conductivity, and mechanical stress as a function of the carbon content suggest that the properties of films with low carbon concentration are mainly controlled by the incorporation of sp 3 hybridized carbon. These films have good optoelectronic and structural properties. As the carbon content increases, the properties of the films are determined by the concentration of sp 2 carbon sites.

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