Recently, there has been an increasing interest on the influence of the deposition parameters on the mechanical properties of materials used in the microelectronic industry. Parameters such as stress, elastic modulus and coefficient of thermal expansion,CTE, have been studied more often since they are important for the development of stable devices. In the particular case of amorphous semiconductors, there is little information about these properties and more research is still necessary to explain some phenomena that take place in these materials. In this work, the coefficient of thermal expansion and the biaxial modulus of amorphous hydrogenated silicon (a-Si:H) and germanium (a-Ge:H), determined by the thermally induced bending technique, were investigated as a function the network strain and coordination number. The network strain, in terms of the macroscopic stress, depends on the deposition technique and preparation condition, while the coordination number depends on the hydrogen content. We observe that the coefficient of thermal expansion of a-Si:H and a-Ge:H depends on the network strain. For high quality films, which are compressive, the CTE is higher than that of their crystalline counterparts. The structural changing from the crystalline to the amorphous phase and the changing on the coordination number appear to interfere little in the magnitude of the expansion coefficient. On the other hand, the elastic modulus depends on the coordination number following the model proposed by Philips.

This work was supported by Brazilian agencies FAPESP and CNPq.