Thermal Strain of In films deposited onto Si and GaAs Substrates

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An investigation has been carried out of the thermal strain in In films deposited onto Si and GaAs substrates at 300k and 77k and then cooled down to temperatures as low as 20k. The strain in the In caused by differences in thermal expansion of In, and Si and GaAs was measured using X-ray diffraction techniques. Also the magnitude of the strain at 20k was found to approximate the strain value calculated from the difference in the thermal expansion coefficients using the biaxial strain model. For the In films, the crystallographic anisotropy both of the thermal expansion coefficient and Young's modulus was considered in calculations. The surface morphologies of In films evaporated in a vacuum of 10^<-7>-^<-6>were changed from island to continuous structures. The continuous films were obtained after that pre-evaporation of In was carried out in a vacuum chamber. Therefore, the change of film morphologies appeared to be caused by the oxygen concentration in the vacuum chamber. The thicknesses if In films were 100 to 140 nm. Since the thermal expansion coefficient of In film was greater than that of Si and GaAs substrates, compressive strain in the vertical direction of film was occurred according as the temperature was down room temperature to 20k. The measured and calculated strain values have a strong dependence on the crystal orientations. A large strain of -1.0%was obtained for (001) oriented grain and small strains of -0.6%were (111), (001) and (313) oriented grains. The dependence on the grain orientation of measured strain values was well agree with calculated strain values. Although the measured strain value were increased as the thickness of films decreased and films were more continuous, the measured strain values merely reached to -70%of the strain values expected by calculation. This mean that the film occurred the relaxation by plastic deformations.